Our Last Time Benchmarking Ubuntu 32-bit vs. 64-bit
CompileBench is a bit of an extreme case, but using x86_64 can be much faster due to additional registers, assuming the presence of at least SSE2, etc.
It depends upon the game, but most titles do not benefit much from 64-bit.
More wins for x86_64... As we're used to seeing over the years. But whenever running these tests, at least some users seem surprised over the difference.