OS X 10.10 vs. Ubuntu 14.10 vs. Fedora 21 vs. openSUSE Factory
The three Linux distributions with EXT4/XFS were all running much faster for the PostMark disk benchmark than OS X 10.10.1 with the Journaled HFS+ file-system.
Fedora 21 was running faster than Ubuntu 14.10 for the Nexuiz game. Fedora's faster performance than Ubuntu is likely due to using the newer kernel (Linux 3.16 vs. 3.17) and it's also using a newer Mesa 10.3 point release. Nexuiz failed to run on openSUSE for unknown reasons.
OpenSUSE was able to run on Urban Terror and there it was faster than Ubuntu 14.10 and Fedora 21.