Actually I think it will be pretty close between the two, the Shuttle is clearly not the better but it will be about on a par for most things. It is true that the A64s CPU is better in most instances but the Ram won't make much of a difference unless you are clocking, the graphics cards will perform about the same(i'm assuming your GTO2 is at about X850 XT speeds? overclock the 6800gt and you are already there as well).