I'd like some help in understanding the state of Nvidia drivers and OpenGL performance.

I built a multi-seat computer based on two 8400GS PCI-E cards shortly after Ubuntu 8.04 was released. It worked very well for many years. Occasionally, in a normal single seat config, I'd try out a new distro. It always seemd 3D/OpenGL took a dive.

Ubuntu 8.04 (NVIDIA GLX Module 169.12)
glxgears 4240fps
glxgears maximized 430fps

Ubuntu 11.04 (NVIDIA GLX Module 173.14.30)
glxgears 1120fps
glxgears maximized 145fps

Is this easily explainable?
Are new drivers optimized for new cards at the cost of poor performance for old cards?
What additional information should I give?
Magic xorg.conf tweaks for the newer driver?

Thanks for any help,