IMHO its impossible to compare the two headphones side by side. They should be keept the far away from each other like matter and antimatter. Because if you A-B the two, HD650 will lose, every time. As it loses against DT880 or K701, or even some technically inferior, but bright headphone, at least for for me. It just seems like its too thick and somewhat veiled when you compare them directly to bright headphones, which often fool you and make you think they have more detail, or more clarity, but that's not always the case. All I know is that when I listen to HD650's for lets say 3-4 days in a row, they impress me more than when I listen to T1's for a few days, to get totally used to their sound signature. I've never had a single WOW moment with T1's. Might be because I don't have a high end amp, but from past experiences with various headphones, I don't think they'd totally transform and do a night and day shift, and thats what they need to do in order to impress me or justify their price. As of now, if DT880's cost 350 dollars, then IMHO T1's aren't worth more than 500. Diminishing returns is strong in this one. :P
Actually they do have a night and day difference with amps. They sound like crap out of the Bellari, but amazing with the Mjolnir and higher quality OTL amps. You just haven't given them a chance yet.