I recently got to compare (in quick succession) the HD650, LCD-2 (early version) & LCD-2 (w/Fazor), all using the same amp and dac, at an LA mini-meet about a week ago.
Even though I have heard all the different Audezes multiple times before, I had never had the chance to do a direct A/B comparison with the HD650. As a previous HD650 owner, I was really shocked at how much better the LCD-2's sounded (to my ears, anyway).
I had forgotten how super-smooth and somewhat recessed the HD650 sounded, but it is a sound signature that I no longer like very much. But I understand why so many people still love them. They can make just about any recording sound "good".
The LCD-2's had a much more up-front and clear sound quality, which is how I now prefer headphones to sound, but it will be much less forgiving to harsh, dynamically compressed recordings. And let's not forget, they are twice the price of the HD650's.
The difference in sound presentation between the two different LCD-2's was fascinating to hear for myself. The early version LCD-2 had a very focused and somewhat narrow soundstage, more of a closed-in, conventional headphone soundstage quality. The Fazor version LCD-2 had a soundstage that was much more open and panoramic sounding, but the expanded soundstage also caused the imaging to become somewhat less precise and more diffuse sounding. To me, the Fazor version wasn't definitively "better" that the earlier version. They both had their strengths and weaknesses. But I could happily live with either one.
Hope this helps.