I have a question for you guys with hd600's. Have you heard the hd650's and how do they compare? I remember I once went to my local headphone shop and tried the 600s and 650s side by side through my iPhone (the amp was being used by someone else) and I must say I definitely liked the HD650 more. HOWEVER, I still have yet to try both of them amped. I only recently purchased an E9 and i think it took the HD600's to a whole new level. I wonder if I would still like the HD650's more though.... guess there's only one way to find out.
Don't bother. The difference is mostly placebo. If it was possible to ABX them, the majority wouldn't be able to identify them.