I'm trying to play L4D2 on Ubuntu 12.04.4 with the FGLRX Post-Release Updates driver installed through System Settings -> Additional Drivers, but it's stuttering like a bitch, and is having input latency issues too. Last time I tried playing a Source game (Half Life 2: Lost Coast) on Ubuntu 12.04.(3 I think) with my old Radeon 3450, it had major input lag with FGLRX, and the open drivers were just far too slow to use. My current Radeon 7850 is a rock solid 60 FPS with maxed settings on Windows 7 x64, but sadly my attempt to move back to my preferred OS is yet again being hampered with gaming issues.

Here is a video of the issue. YouTube's video processing has made the game look likes it's running smoother than it actually does. And sorry I couldn't record fullscreen, but the screen recorder I used didn't work unless I used windowed mode. Anyway, the link: https://www.youtube.com/watch?v=kpx8wRXvaoM

Thanks!