Re: 2 Video Cards -- Disable Open GL on single?
The GeForce GT 520 is from the Fermi family of chips and the 8600 is from the previous family, so that explains the mismatch. How exactly is OpenGL failing on screens 0 and 2?
To disable Composite, you need to put the option in its own top-level "Extensions" section, not a SubSection of a screen. You can't disable it on just one screen and not another because extensions are server-wide.