Windows 8.1 vs. Ubuntu 14.10 With Intel HD Graphics
First up with a classic OpenGL game, OpenArena, the performance under Ubuntu 14.10 and Windows 8.1 was virtually the same -- Linux was faster by one frame.
The frame timings were nearly identical too between Windows and Linux for this ioquake3 game.
When running Xonotic with low image quality settings, Windows 8.1 Pro was significantly faster than the Intel Linux driver found on Ubuntu 14.10 (Linux 3.16 + Mesa 10.3). Using the Linux 3.17 kernel and Mesa 10.4 did improve the situation in being 24% faster than the stock configuration of Ubuntu 14.10, but Windows 8.1 with the newest Windows driver remained 62% faster.