The HP50's are considered excellent for classical music; check out the review by Headfonia.
If you have a small head, maybe look into the smaller versions of the K550's, the K551's and the even more portable and stylish K545's. The K545's were on my shortlist, but I think they might be too diminutive for my 'Elf' ears.
Honestly, if you're new to headsets and headphones like I am, don't be afraid to experiment. Find a few cans you like the visual style of, are on sale, have the features you require (such as closed-back, detachable cable, carrying pouch, etc.), and have generally favourable reviews, and maybe consider buying a few different ones and sending back the ones you don't get along with as well. Of course, if you like them all, you may end up not knowing which ones to part with. ^_-
And don't solely go by the guide here. It's just one man's opinion, and he hasn't reviewed all the headphones out there. I had to look elsewhere because none of the ones listed fitted my criteria.
If you're confused by the jargon that people use in reviews, so am I! That's why it might be better to focus on features and price more so than sound signature. Because let's face it, basing your opinion on another person's interpretation is rather silly by definition. There are so many factors that need to be considered, such as source music, amplification, how tight the seal is, etc. Then of course you have the myriad of different ways the human ear is formed based on your DNA.
I've not tried the X1's so I can't say how well you will get along with the lack of isolation. It's been on my mind as well. I live in Ireland, though, so returning items bought from Amazon or elsewhere is expensive and not easy. Otherwise I'd buy them and see for myself whether I can live with the noise or not.