I'm not going to bother overclocking my GT, as it runs all the latest games on highest settings, 1600x1200, AA, AF etc etc.... silky smooth. Why would I bother chancing a fucked warrenty, just for a few extra 3dmark points to look at???
Still, it's nice that it
can overclock (usually) for the future. But really, there's no game that's out yet, that's going to show any humanly noticable difference, between the GT & Ultra. (2-6 fps in benchmarks: WOW!)
Anyway, you've got one of the best two cards out. It sounds like your under the impression that the X800 is the better. But that's just a matter of opinion. They both win at different games and every benchtest that tests up to around 10 games is in danger of showing misleading results, depending on the game they test with.
Basically, what the hell are you worried about? ATI have been working closely to valve (just as nvidia worked closely with carmack & id) So when the game first comes out, ATIs drivers will be more ready, but even then, your card is going to be the second best, you could have. Then, just wait a few weeks for nvidias new drivers and there won't be much seperating them. (Same thing happened the other way round with doom3).
Anyway, don't worry about it, ffs
