OK here is what my First Impression. I just got it today, so my opinion about sound quality and comfort may change.
I have recently bought QC35. I got wired P7 as well. I got numerous other headphone including PM-3, HD650, good old QC15, Focal Elear, etc.
I used MDR-1000X before, but their touch gesture system is pain in the ass, so I returned it.
I am trying to compare with P7 and 1000X, since they are main contender, but 1000X is not with me, so I won't talk about SQ of 1000X based on memory.
SQ : I definitely sense less bass than P7 and QC35. PX has about right amount of bass what I call more neutral. I do not want to say PX is completely neutral at this point, but it is closer than Wired P7 and QC 35. But do I like better than QC35? No... They are roughly similar level IMO.... but I slightly prefer QC35 at this point.
Comfort : Bose clearly wins. softer earpad, lighter weight. Though there is good part about PX. Earpad side thickness is narrower, so earpad put more pressure on contact area but it provide more area inside of earcup, consider size. Thus, ears are getting less interrupted than Bose does. Plus angle movement of PX is quite good, and clamping force is adequate. PX is heavy though. Overall I prefer PX comfort over MDR-1000X. 1000X had pretty bad comfort for me, especially bad with my glasses.
ANC : PX is probably worst among those 3 in this area. It's not PX has bad ANC performance. Truly Bad NC heaphone amplifies noise frequently. PX does not do that. It does decent ANC job. But competitors stand strong. QC35 and 1000X have impressive NC performance while PX does not. For me, ANC of PX may be considered decent, but nowhere near great, especially nowadays.
Finish : PX wins. You can see numerous screws on QC 35 while you see zero screw on PX. Bose uses synthetic leather(though I think it is more comfortable), while PX uses real leather. Not saying QC 35 has bad finish, but it definitely lacks premium feeling of PX. Even mic. I can see bose has holes all over earcups. I know we need those holes, and more holes mean more microphone built in for better NC, but at the same time, it ruins outlook IMO. PX has microphone hole top of metal portion, and it is nicely done. MDR-1000X does not premium feeling of PX as well.
ETC : PX has proximity sensor, and I admire that. If you lift your earcup, then music stops. When you put back on, music starts back. Though I would love to see function to not automatically starting music when I put headphone back on... while it turns off when I take off. It also able to turn on sensor/turn off sensor, and change voice level during ANC is ON. It always took time to communicate with headphone when I turn on app, but I can live with that. As a glass wearer, proximity sensor can be annoying as well, because when u just want to relocate headphone due to glass issue, music stops easily. Even Low setting of proximity sensor does not prevent this issue.
Overall, I think PX is not the best ANC wireless headphone. I think QC35 is the best. IMO, SQ of all 3 are quite comparable level, and it's more about personal taste issue. Though this is my first impression, so my opinion about SQ of PX can be changed. But other than SQ, Bose QC35 wins comfort and lack of glitches. Sure you can turn off proximity sensor of PX, and considering comfort of PX is not bad at all, it is still strong contender, especially with B&W branding and premium finish. I still think PX is at least good NC headphone, and it can be decent wireless headphone as well. But I think PX needs extra edge to beat QC35. I hope firmware/software update will help PX. I personally love B&W, and their premium look. I have QC30 to cover ANC intense moment such as flight travel. Better ANC performance is nice but not desperate for me. If I like SQ of PX just little more and if there is little better software, then I might choose PX over QC35... but I dunno. I only need one full size ANC headphone. At this point, my heart is saying return QC 35, but my head is saying return PX instead