I'm a little late to this conversation, but I can help point you to a couple options or at least confirm some that have been mentioned.
You speak of timber a lot. I understand why. Many IEMs, especially BA based ones tend to have almost too clean of a note, at least a note of very short rise and decay with minimal body. You may have BA earphones that are thick bodied like the Triple.Fi 10 or BA earphones that are very articulated like the W3, but it's tough to find a product that sounds "real."
As ways already said and you have come to understand, it's really about everything: the speed, the dynamics, the articulation, the body, everything. It all comes together to create a believable presence, something that sounds life-like. At least that's the goal anyways.
Speaking of timber, and I will add terms like texture, articulation of note, and body as they sort of go hand-in-hand. It's all about fleshing out the note, not only filling the presence but also articulating and detailing the information to portray the information fully and accurately. The better it's done, the more life-like or at least more true to the source information it becomes. In the end, you may not want to discuss just timber or even timber at all. You might simply ask, what is the most life-like, more realistic sounding earphone you've ever used? What was so good in reproducing the sound that it could literally fool you into thinking what you heard was real (background noise in a song, somebody talking in the background in the audio track). I can't say I've owned too many earphones that had a very life-like sound, something I could describe as sounding very realistic. The list is short, and that is kind of unfortunate. Notable earphones that I've used include my old and much loved Yuin OK1 earbuds, the now discontinued Denon C700/C751 (unsure how the new models relate back to the previous gen stuff), the Audio Technica CK10, the squeaky clean SE530, the colorful Triple.Fi 10, and the not yet publicly available RE262. There are a lot of other great earphones, but they fall short in portraying something that can be believed as sounding real and life-like. Even the ones I listed vary some in how well they present a realistic sound and include some shortcomings. The OK1 is a bud, very good, but not an IEM. The C700/C751 isn't the sound signature you're looking for as I see it as a poor man's IE8 in many ways. You don't want bass that strong. The SE530 is great for realism, but it's just too clean and short on note. You get a life-like sound that ends up just a little hollow/ghostly. The Triple.Fi 10 is both bassy and bright, and you want something colder and more mid-centric, although EQing can improve the balance. Even so, it's still a thick note with limited dynamic breadth and more fun than analytical. The RE262 is very good but borderline too clean like the BAs and less analytical with its smoother top end. In the end, the only one I see seriously fitting your goals is the CK10. Short a moderate but narrow treble peak at 10kHz, it's very flat, and note quality is very high through the entire spectrum. It's a BA but very well articulated, dynamic, and well fleshed out. The portrayal of realism is very high. The bass isn't overpowering. It's super fast and extremely detailed. Maybe the only shortcoming I might give to it is that it lacks some of the visceral sense as many BA based earphones do, but the presence is still good enough to sound real. Some gain in visceral presence can be had by EQing sub 40Hz frequencies to which the CK10 does roll off some with.
What about tricking the mind? What's good enough to make something sound real as in real world real? One thing I've seen with a couple earphones I've used is that they tend to be good enough to fool me into thinking a noise or talking in the song or video I was watching existed in the real world, enough so where I'd do something like take off my earphones to see who was talking to me. I will say right up front, most earphones I've used are not capable of this. They simply aren't transparent and believable enough to pull off such a stunt. You always know you're listening to an earphone and the sounds you hear are coming from the earphone. Even if the transparency is very high, it may not be good enough to sound that real. The only earphones I've really had that were that good were the OK1 earbuds and the RE252. Frankly I like the OK1 buds a ton. They do a lot of things incredibly well, however they are buds, and they do have certain shortcomings too. Why didn't I liste the RE252 above? Well, it isn't universally life-like. They dynamics are compressed enough where the sound comes across constrained and slightly closed in. The trickery comes from its great ability to portray subtlety in music and sounds very well. This at times can catch you off guard. However, the overall presentation suffers from a dynamic driver that is constrained in some way, be it a weak motor, high loss suspension, or something along those sorts that limits the effortlessness and subsequently believability of the sound as real and life-like. The RE262 does it better. The RE262 is even more transparent. However, the RE262 falls short in that it is almost too clean and lean in note. I wouldn't call it ghostly like the SE530, but it does start heading that direction a little bit. Why not the CK10 if it's so good? I don't know. Frankly I can't tell you. From a technical standpoint, the CK10 does almost everything right. At the same time, it simply isn't engaging, visceral, radiates sound like that of some of these other earphones. The transparency is outstanding, but it doesn't just "exist." The earphones you find that can fool you better are the ones that the sound more so just exists rather than is created. The sound is just there, more like you're thinking or daydreaming the sound rather than hearing the sound. This is something the OK1 earbud does. The RE252 does this to some level too. I will say the RE262 heads towards this degree too.
There's a lot of talk about the Ortofon earphones. What about those?
Well, if you want timber, they have it. If you want balanced and something more clean and analytical, they fit well. Speed is good. Dynamic range isn't outstanding. Quite information is extremely quiet, but it does portray loudness well. It's just not the most articulated nor linear in behavior. There is a natural sense of realism which is good, but the presentation of that sound in the sound stage isn't believable. The sound stage ends up a little small and lacks depth. Apparently the e-Q5 is improved, but I have not heard it personally.
Any other noteable suggestions?
Sure. I really like the CK100 a lot. It's very well balanced, broad in response, very fast and detailed, and offers good presence. It falls short though in the typical BA way, lacking texture. In this case the note is hearty, sounds full, but the note isn't well textured/articulated, and the realism is sucked out. It's sort of like the SE530 but from a different direction. The SE530 had great dynamics and could articulate, but the note was super short and prevented the earphone from really fleshing out the sound. The CK100 on the other hand fleshes out the notes well but doesn't articulate the notes hardly at all and suffers from a lack of information in another way. Both are good examples of a potentially outstanding product cut down by very specific shortcomings. Really, a lot of these earphones are like this, doing tons of things really well but falling short in this key area or that and suffering from it.
So who wins?
Well at the end of the day it mostly comes down to personal preference. However, if one was to set aside personal skew, it comes down to the earphone that is the most technically correct, and that pretty much is the CK10. If you could forgo one fault here or there, a lot of other earphones would end up being extremely good choices. However, you do have specific goals, and for that, I kind of see the CK10 as still being the best.
What about the OK1 bud?
It's an earbud. The driver is quite good, extremely detailed, transparent, textured, great realism, etc. For that, it's a great product if you didn't want an IEM. It also requires amping, powerful amping, and does benefit from EQing as the response isn't ruler flat nor as extended. Versus the CK10, I can see the CK10 as being a better selection due to a number of reasons. Still I have to say that my earphone approach has been me buying a pile of products, testing, comparing, and selling off what didn't suit me best. I sell until I'm back down to one product. Then I buy some more to try out and compare. Every time I've gone back to one, I've always been left with the OK1 earbud. I've kept the Ok1 over the ER4S I owned and over the RE252 I owned. The CK10 I had wasn't mine but borrowed from Joker, so I can't really say which I might have seriously kept. I wasn't compelled to make that choice. Even now I own the e-Q7, CK100, UM3X, Triple.Fi 10, RE252, and RE262, and I will soon work my way back to one product. It hasn't yet been the time to really decide which one stays, but the OK1 has a good track record and is currently the title holder. Why talk about the OK1 so much? Well, if you don't actually need an IEM, it might be something that suits your goals. Would you be better off just sticking to the CK10? Perhaps, but it's hard to say. I think there's a lot of really great products out there, many that at least I could be happy with if I only had that one. I think you could be to with a small variety of products that suit your needs well.
