hahaha I haven't heard the last two. I've heard the Momentums & I think they will do great w/ classical. Note I do not personally really listen to classical though.
I imagine any pair of well balanced (non-bass boosted/non-excessively colored) pair of headphones will be great for classical lolol. edit: i guess I would personally pick the k550 to be especially amazing for classical due to its great sound stage & crisp clear treble & well-balanced sound signature.
obviously open headphones would be better, but since you want portable use, then you have to go closed. Out of the closed options I've personally tried, I would say go K550 (not really very portable though... need to look at the other varients K551/K454) or Momentum Over-Ear. The B&W P7 is overpriced in my personal opinion. i've heard great things about both the nad visio hp50 & keef m5000. perhaps it's time to go demo a few different pairs to see. there really is only so much you can get out of reading other people's personal subjective impressions online. the best way to tell what suits you is to try some stuff :) good luck yo.
Mmm, thanks. Yea, need to find a meet somewhere to try all this.