When testing KDE and Xfce, in none of the OpenGL games tested across Windows 8 and Ubuntu 13.04, did Xfce or KDE (with suspended effects) provide for any new wins. Canonical has improved the state of Unity and Compiz so that it's no longer a very sore point for Linux gamers compared to other desktop environments, as already shown for Ubuntu 13.04. Using Unity was not the reason Ubuntu 13.04 lost to Windows 8 with the Intel OpenGL driver comparison.
For those not liking the selection of cross-platform games used, it's what was known to work well on both operating systems with similar renderers, e.g. using OpenGL and not DirectX and when testing with the highly-optimized proprietary AMD/NVIDIA drivers that are largely common code-bases across operating systems will yield comparable frame-rates. For the Source Engine games, there are still ongoing Linux performance optimizations and also still some Steam client problems with the automated benchmarking process for the side of it. If you feel differently about the tests, feel free to run them yourself using the Phoronix Test Suite or writing your own OpenBenchmarking.org test profiles to cover other areas of 3D performance.