Stock GT = 350/100. Stock Ultra = 400/1100. Stock Ultra Extreme = 450/1100or1200. Anyway, the way you OC is work your way up slowly, testing every change with Game 4 in 3DMark03 (or any other REALLY rigorous benchmark, Doom3 maybe). Most GTs I've seen can reach ~420/~1150, but don't be disappointed if you can't get there, you paid for a card that runs at 350/1000, NOT at Ultra speeds. Go up in 10MHz increments till you hit 390/1080 or so, then go up in 5MHz increments till you hit your max (then back down a bit).
Chances are you can get a li'l higher than Ultra clocks (not the ones you listed, the ones I listed). Don't count on going much higher or doing the BIOS vmod w/o better cooling, however.
Maxtor disgraces the six letters that make Matrox.