https://bugs.freedesktop.org/show_bug.cgi?id=52345
--- Comment #4 from Amadeus sha256sum@gmail.com 2012-07-21 19:13:08 PDT --- I see.
If I do
glxgears -geometry 1600x1024+0+0
then I get 40 FPS in both cases instead of 60fps. It takes ~3% CPU.
If I start a 3D game in Wine, it feels the same (very slow).