Sorry didn't realise I couldn't post link, that's fine warning accepted.
Bang for buck is subjective, but superior quality over a long period of time, and if you look after them they could easily have a 20 year+ lifetime, nothing beats them. Cables are modular as well (one plug in each side so no annoying wires flapping around), and replacements easy to order.
After they are broken in, the comfort is very good. The best headphones for comfort where the HD590's, very good quality and they float on your head, nothing beats them on comfort. 650's are tight at first, but leave them between some books to stretch them and they become very comfortable and non fatiguing.
I swear by them. My hi fi cost me around £5k and these £300 headphones are very close to the quality of sound that comes out of that. They seriously are the best product, I have ever bought, ever.
If you look you can find them for <£200 as well. I think mine cost £180 brand new in some sale.
Only problem is you can't skimp on a soundcard.