my short specs:
AMD Athlon 64 3400+
1 GB Ram
The scene contains some very large textures and is lit by a lightdome casting buffered shadows. No raytracing is involved. The OSA is set to 16. Here's the output, the rendering times follow below:

the times:
- win32: 1min 27sec
- gentoo64: 48sec
Before the usual "unfair comparison"-posting starts let me mention my intention (ha!):
This test is intersting as it compares stable, tested and non-customized systems and software-builds. Everything I used works out of the box (if you consider gentoo "out of the box") and is proven to be stable and secure within a production-environment.
For people like me, who prefer to use software rather then compile it this comparison might be meaningful.
Cheers,
Konrad