I've had both, hd800 and t1. I think the t1 had much more air, just more musical. The hd800 sounded dead. Couldn't listen for more than an hour.
The HD800 has it's place for me primarily for acoustic and less cluttered recordings, the T1 on the other hand sounds great with just about anything.
If anyone is in the market for a high end HP, the discounts on the Tl are much better than just about any other high end HP at the moment, just a no brainer as a purchase.