Nice choice Stan. I owned the HE500 at the same time as the hd650. The 650 was sold a week later... It was the more focused imaging and clearer- smoother sound that beat them for me. Plus they have one of the best treble out there ime. I much preferred them with the velour pads over the pleather as this made them a little more airy.
I've never compared them against the hd600 side by side, so I'd be interested in your opinion.