I currently own both, and think the both have there strengths and weaknesses. I am very happy to own both.
+1.. Although i prefer the he500 on my 337 i must admit the hd650 has its pros..i can imagine the hd650 siunds better on a smaller otl tube amp then the he500...u have to look at the complete picture..what kind of rig u have,what music u like, how important is comfort for u..and so on and on..put all those dots together and then listen to phones who are wellknown to work well with that..take a couple of them ..and then listen well..and keep the one who makes u being thrilled..the one who even makes u listen to music u normally dont like but just because the musicians in the songs are magicians on their instruments or with their voice...and u just wanna feel an hear that for real in that phone..sometimes its not the price who determines whats best for u..imho