Just adding my data point to the mix. Been an XM4 user since day one. I have liked its sound a lot, for a set of TW buds (which I don't expect a lot from). I personally want a set of TW buds to sound well enough from point A to B, and the XM4 had decent detail, a great sound stage, and separation. However, my biggest gripe was its dark signature. The low end was too bloaty for my tastes, and the high end a bit recessed. I noticed it everytime I used them, but the other redeeming qualities kept them in my pocket, along with the fact that they could fit in the small coin pocket of my pants (albeit, tight fit).
So when I heard the XM5 had a more balanced sound, I had to get it. I'm not one of those who had fit problems with the XM4. I actually had a good fit and seal out of the box with the medium tips. The only time anything was ever an issue was on long flights, where about at the 3 hour mark I could feel a slight pain developing. But after a short break I could resume. So fit wasn't really a factor in me upgrading, it was purely sound quality. In other words, if the XM5 sounded pretty much the same as the XM4, I would've stayed with them.
Much to my delight, it is true that Sony really refined the sound of the XM5. It is quite a difference to me. Clarity is so much improved. The muddiness is eliminated. I was surprised hearing from some users that the bass is toned down. I don't hear that. The bass is still quite bold/present, but it's wonderfully controlled and doesn't bleed.
The mids also surprised me, which aren't the typical recessed quality that I've seen from Sony (even on their top-end IER-ZR1). It's now balanced with the rest of the spectrum. I need to do more listening, but the treble sounds great to me to, less recessed and clear. I haven't gotten a sense that the soundstage is larger than the XM4 as some people have said. It's about the same to me, but it's fine as I always thought the XM4 had great soundstage and good 3D effect (as opposed to a flat, 2D sound on cheap buds). On sound quality alone, it's my opinion that Sony knocked it out of the park. To me, these have left TW buds territory and entered real IEM territory; quite the feat.
Not all is rainbows and sunshine though (is it ever?). I would say that their design is a complete step back. I'm kinda taken aback by it actually. You don't often see products go backwards to this extent. The buds feel much cheaper than the XM4. They feel just like cheap buds, of which the glossy material adds to. They also don't have that authoritative, magnetic snap when you put them back in the case (again, like cheap TW buds).
This unfortunateness extends to the fit. Where Sony designed the XM4 more friendly to bigger ear people, rather than strike a balance, they've gone in the other direction and made the XM5 for small ear people. I don't have super picky ears. I'm usually able to take a new earbud out of its box, with the standard tip size, and it works just fine. A seal for me with the medium tips of the XM5 was in no way possible. Their medium is like a small, so their large is like a medium. So I was praying that the large would work for me, cuz there's no more after that. Unthoughtfully, there's an extra small in the box, but not an extra large. Fortunately, although the large tip is still slightly smaller than I would prefer, I'm able to achieve a seal, but this is only really jamming the buds in my ears. I think Sony needs a larger sample size to test the fit of their buds in development, they seem to be struggling with this.
Apart from this, they seem comfortable. I haven't tested them on a long flight yet, but I suspect it will have long-use comfort. Hope these impressions helps others deliberating these buds.
