some time ago I noticed big FPS drop with 3D game on Ubuntu 12.10 and recently in Mint 15 as well.
It depends on which window manager being used. When using cinnamon or any other 'fancier' manager my FPS show 30 (feels like 15), while in Open-box, I get 60 FPS (which also feels like 60) on the same situation.
The game is Live For Speed (demo) under wine. Since Open-box does not use acceleration (I think), it looks like other window managers are keeping CPU/GPU busy for no reason (all WMs have low CPU usage). Or can they strip capabilities from 3d app?
Are there known driver/WM/kernel or X11 architectural issues that can explain this?