glxgears is dramatically not a benchmark. Its fps output measures nothing interesting in the real life. You should use a real 3D game or whatever, but not glxgears.
Alright, I admit this bug is invalid. I've run gtkperf, the best I could find in Debian, and observed no statistically significant slowdown. Tried to run these demos/benchmarks <http://unigine.com/download/> but couldn't because they require the GL_ARB_map_buffer_range extension — don't know what it is, but it sure isn't in my glxinfo output.
-- Alexey Feldgendler <alexey@feldgendler.ru> [ICQ: 115226275] http://feldgendler.livejournal.com