This video is a rebuttal to a video put out by Mwebgamezone. The tests were done on the same system with nearly equivalent configurations. One difference is that a slightly older graphics card driver is being used on the Windows 7 install (327.23 on Win7 and 331.20 on SteamOS). Since this video was recorded, I upgraded the driver on the Win7 install to 337.88 and I am getting roughly the same results. At least for this benchmark, the two configurations pretty much performed equally well.
Some hardware details:
CPU: AMD FX 6200 @ 3.8 GHz
RAM: 8 GB
GPU: Nvidia GeForce GTX 550 Ti 1 GB VRAM
OS: Steam Beta update 118 / Windows 7 SP 1
Mwebgamezone video https://www.youtube.com/watch?v=XY3oezBl-oM
Update: Since updating SteamOS to update 120 (using the 337.19 Nvidia drivers), Linux now slightly outperforms Windows 7 in this benchmark. The difference is minor though. https://dl.dropboxusercontent.com/u/31073509/Unigine_Heaven_Benchmark_4.0_20140709_1546_SteamOS.html