Here are some benchmarks comparing Windows 8 to Linux Mint 15 (Ubuntu derivative). I fully expect Steam OS to perform similarly to these results. This is my hardware, so your results will vary but should scale according to the components that you use.
Here are some caveats to keep in mind while accessing the data. I obviously used the exact same hardware. On Windows I used the 327 drivers, but on Linux, the 325. According to Nvidia these drivers parity each other for the most part so this should not be a huge factor in the conclusion of the results. I also ran three passes on each with one warm up pass to let the GPU get to operating temperature. I was going to average the results but it turned out they were nearly identical within .3 of each other so I used the third pass on each OS.
Windows 8.1 was released today but I could not use the update. It turns out that OpenGL is bugged and does not run correctly. On the Linux side, it would have made much more sense to have used Ubuntu considering that is what Steam has been officially supporting but Linux Mint is based on the Ubuntu core. So there should be very little difference between the two.
Now on to the benchmark. Most of the details are in the pictures provided below. If you feel like I missed something please leave it in the comments.
|Result and Details|
|Linux Mint 15|
The results are well within margin of error for each other so I think it's safe to say that you can enjoy gaming on either Linux or Windows without losing any performance. This looks good for the future of Linux gaming and Steam OS. With Valve heading the way, you can expect that the hardware manufacturers will produce even better supported drivers for Linux. An area that historically has been severely neglected. Now the waiting game begins on the developers to release the titles on Linux and hopefully not half-ass ports.