Testing got underway with ETXReaL, the heavily modified open-source Enemy Territory code-base that boasts many improvements to its renderer. When moving just from the 304.51 driver release to the 310.14 driver there was a 6.5% boost in the frame-rate. However, the GL threaded optimizations for this game did cause a measurable performance drop.
For the DarkPlaces-powered Nexuiz, there's a 12% improvement in the frame-rate from simply upgrading the driver. However, when attempting to take advantage of __GL_THREADED_OPTIMIZATIONS, the frame-rate was more than chopped in half.
For OpenArena it's the same story of the default 310.14 driver configuration being faster than 304.51 while trying out the threaded optimizations led to a big drop in frame-rate.