Perhaps... We could focus this thread on the two problems "Gabe" mentioned (on steamforlinux.com):
1. L4D2 runs multithreaded at 250 – 300 fps on my Windows 7 machine. Single threaded it’s ~180 fps. On Linux it runs at 25 – 30 fps with the same NVidia GTX 580 video card (after getting them to fix some things), and around the same on a ATI 6970.
I've had performance issues with L4D2 on Wine. To the point where I don't try playing it. At the same time CS:S/Portal are both easily playable.
2. Good tools to track down OpenGL performance and help debug rendering issues just don’t exist.
Some of these tools, have not yet been mentioned and do run on Linux. Anyone experienced in OpenGL debugging, want to see if these could help?
Of course, if they would release a development version, we might be able to help a lot more...