and due to the bios of the video cards being different, i dont think that the nvidia drivers will let you sli them. the whole point of sli is to use 2 identical cards. wait to see what others say, but i think flashing the gto to gtx specs is your only option.
This process will allow any 24 pipe G71 card to work with any other. This includes 7900GT, 7900GTX, 7900GTO, and 7950GT. The cards will operate at the speed and framebuffer size of the slowest card / card with least RAM
Well from what Ive learned is that GTO easily reaches 1600mhz because it does not have the GTX's "tighter memory timings". The GTO bios has relaxed timings so reaching 1600mhz shouldnt be too much of a problem but it is not equivalent speed to a GTX bios @1600mhz.
Why don't you just get a GTX? I've found them to be cheaper now than getting a GTO. The GTOs are hard to get hold of.
Well here in canada, GTOs= 280$<>310$ & GTX=410$<>560$