This morning, I overclocked my 8800GT(it's not special in any way, just a plain old 8800) on stock cooling to 700/1750/1000. I didn't even do a Vmod.
I was able to run TF2 stable for 2+ hours at this clock, with a peak temperature of 58*C. Not a single artifact in sight. For some reason I didn't think I'd be able to do that on stock cooling, and without doing any vmod. I suppose the 8800GT is a better overclocker than I thought.
I went on to push it to 750 Core and 1050 memory, until it crashed lol. I can't wait until I get aftermarket cooling and do a vmod lol.