I listened to the HD650s BRIEFLY at the 2007 RMAF and compared them to the HD600s, which I just sold on consignment. I thought that the 650s were significantly better. Those and the AKG 701s may be a consideration in the future.*
*Right now I'm so spoiled by the mains that I just ditched a Stax SRM T1 driver unit with both original Lambda Signature and 404 equivalent earspeakers.