Re: Which is better?
What resolution do you play at? Generally, more memory is favored with higher resolutions (1600x1200 or higher), with anti-aliasing, and other eye-candy effects. I think I've heard somewhere that upcoming games, such as Crysis, are going to benefit from the extra memory as well, but I don't know about Starcraft 2.
Amount of memory aside, the XT is the better card. I say if you're gaming at 1280x1024 or less, especially without anti-aliasing, the XT would be the better choice for you.
ASUS A8N32 SLI-Deluxe, AMD Athlon X2 3800+ @ 2.8GHz, eVGA 8800GTS 320MB, 2GB Corsair XMS DDR400, 160GB WD HDD + 320GB Seagate Barracuda 7200.10, AC Freezer 64 Pro, 700W OCZ GameXStream, NZXT Zero :D
I think I've decided to leave... maybe I'll come back sometime.