I have the Westone 4s and many other excellent IEMs in my growing collection. They are all so different that it is hard to rate them without taking into consideration so many factors. To name a few, 1) the type of amp(s) used, 2) style of music, and 3) personal taste ( the dark horse in this race).
1) Some amps work great with one IEM and not another etc. You will just have to check this out for yourself. If your can’t, you will not go wrong with the Ray Samuels Audio Shadow, or hornet ( or anything else he creates). Also check out the the Arrow (personal favorite), Pico Slim ( too cool - great leather case and oh! so small) and the TTVJ Slim among many others. These all sound great.
2) Music type is a huge factor as well. Do you listen to only classical, or do you like all kinds - rock, jazz etc.? For instance I like the 4s for classical but find they are a bit flat for rock.
Last, personal taste is personal taste and that is the hardest to define.
3) Everybody’s taste is different. Take Shure's venerable SE535, the Westone 4 blows them away in terms of technology. The 4s are also cleaner, more precise and I think a better fit for my ear, but I still like the Shure 535 better ( I got the Comply P-100 which helps). They sound more artistic, and true. The overall design seems better thought out. The cable is also a huge improvement over the 530. As I mention (above) depending on what type of music you listen to, that is a huge factor in what IEM works best for you. I listen to all types music and I feel that the SE 535s are more forgiving and also handles low BIT rates better than the Westone 4s. I have a huge disc and digital music collection and not all my rips are lossless ( although I am getting there). Are you getting the picture her? Lots and lots of factors to consider. Just to put this in perspective I feel the Shure's are only 5-7% better. We are spitting hairs at this level of IEM.
If this was not enough, the Westone 4 are so good that you will not see a drastic change in quality as you purchase any other universal IEM, until you step up to customs. And if you do, the JH13 or the JH-3A are really the only way to go. Jerry is a genius period. That said, I was slightly disappointed that the step up in fidelity does not seem to match the huge leap in price. Keep in mind, on top of the $1,800 I paid I spent an additional $200 to get a great audiologist to make perfect ear casts. Sure, if you have the money to burn go for customs you will not regret them, I don’t. I am just managing expectations. It takes a lot of technology, once you are at the Westone 4 level to beat them handsomely. That is my point here.
Now, to answer you question: If you really want something that will really blow your mind. Something that can cut across all the BS out there, there is one set of phones that clearly sits above the rest. Check out the Audeze LCD-3 and Ray Samuels' Dark Star balanced amp( perfection). I know this is not an IEM, but it is pure heaven and that is what he are all striving for. The LCD-3 and it’s sibling the LCD 2s are open planar magnetic drivers and this is the pinnacle in our field. Full, pure sound that surrounds you. These are open sets so you will hear stuff in the room, but that is really a must at this level. For $2K + $2K for the amp (which is not really that bad) This will - absolutely, positively, 100% without a doubt blow you, your Westone (and your wallet) away... and it is worth every, damn penny. You may not be able to do this now $$, but that is certainly the final destination ( this year at least). Last this is just my personal opinion. There a people on this site with way more cans, amps and knowledge, not to mention free time - I just had to say that
Good luck, man.