Through observation I have noticed that most people don't extend the earpieces far enough out of the headband and this raises the clamping pressure dramatically. The headband should just barely touch the top of the head; if you feel pressure there, it's on too tight and you need to extend the headband a click or two. If this is done, the clamping pressure is perfectly reasonable, though never as comfortable as the 800 or the Beyer Amirons I sold my 650's for (which also sound much better). Materials-wise the hd*00 cleans the 650's clock for sure.
The Amirons are actually the most comfortable full-size cans I've ever had on, even better (for me) than the 800, but the 800 is no slouch and wins somewhat on sound for ~2.5x the price.