Intel Broadwell HD Graphics 5500: Windows 8.1 vs. Linux
First up is the most basic OpenGL test still in use on Linux systems: the ioquake3-derived OpenArena open-source game.
With this basic game, Ubuntu Linux in all tested configurations slightly edged past Windows 8.1 with the newest Windows driver. Of course though, this is only stressing old GL2 code-paths. When upgrading from Mesa 10.3 to Mesa 10.5-devel, the Linux performance seemed to slightly regress.
The Broadwell HD Graphics 5500 aren't powerful enough to handle the Unigine Heaven test in any meaningful way. However, for what it's worth, the Linux performance was right behind Windows 8.1 on this ThinkPad X1 Carbon ultrabook.
With the less demanding Unigine Sanctuary test, Ubuntu 14.10 was running right behind Windows 8.1. The various updated Linux driver configurations didn't provide any benefit in the Unigine performance for this Core i7 5600U system.