x800GTO2 is slightly more expensive than the x800GTO but its GUARANTEED to overclock; in fact, some come with 16 pipes unlocked right out of the box. If you want to overclock, i definitely recommend the x800GTO2. If you're not gonna overclock, 6800gs woulda been your next choice but you just said its too long... and i have no idea about the x1600xt.
x800gto2 can overclock to x850xt platinum edition or even faster, it has the exact same core.
"Is virtue a thing remote? I wish to be virtuous, and lo! Virtue is at hand." -Confucius