While Unigine is beginning to offer their games with i686 and x86_64 binaries, with the 32-bit Unigine Tropics tech demo there is no noticeable performance difference between the different kernel and environments even with NVIDIA's 64-bit binary driver. The Quadro NVS 140M on the ThinkPad T61 was not able to produce any meaningful Unigine results.
Lightsmark has 32-bit and 64-bit binaries. Ubuntu's i686 PAE kernel was slightly faster than the i686 non-PAE kernel on Ubuntu 11.04 with the Lightsmark OpenGL benchmark, but the difference was not anything meaningful. When using the 64-bit binary on the 64-bit kernel, the frame-rate went up a bit more, but again it was not anything significant.
Nexuiz does not have separate 32/64-bit binaries, but the difference between the kernels was insignificant.