I don't think they ever fully sorted the compiler issue. From memory the windows compilers they use tend to combine sections of the benchmarking routines, effectively giving a higher score than the same equipment on linux. The 'nix compilers are, less aggressive I suppose, and return binaries that are closer to the original intent but give a comparatively (slightly) lower benchmark score. From my experience, however, the linux clients return more work. Slightly.
Based on that, if the points are more important to you than the work, use winblows. If you're in it to help cure cancer etc, use linux.
That's just my opinion, make up your own minds.