So I don't have any amd64 processor at hand right now
Meanwhile, a thread about this benchmark in gentoo forums was opened. I think you would like to take a look
If you would like to try gentoo, AMD recommends (http://www.amd.com/us-en/assets/cont...docs/32035.pdf)
these CFLAGS="-O3 -ffast-math -funroll-all-loops -fpeel-loops -ftracer -funswitch-loops -funit-at-a-time"
Another interesting link: http://enterprise.linux.com/article....413209&tid=121
Look at these benchmarks and read the comments
These results, despite being gentoo based, are not optimal just because the packages were compiled with march=pentium4. march=athlon64 should be used instead.
This is what happens to most of binary packages based distros. They have generic (safe) x86_64 support.