First up for the non-OpenGL benchmarks is looking at the GPU temperature as the system idled at the Ubuntu 11.10 desktop with each GPU/driver combination.
The GPU thermal results while idling are somewhat surprising. While there are many Nouveau users that report warm laptops, overheating, and other thermal-related issues when using the Nouveau driver, with these discrete desktop GPUs there was not too much of a problem. When idling the GPU temperature was close to the same under both drivers, for most of the graphics cards. This, however, may be due to the graphics card fans all running at full-speed when the Nouveau driver is in use. The exceptions where the Nouveau performance was worse was for the GeForce 8400GS and GeForce 9800GTX.
The NVIDIA GeForce 8400GS used for testing was passively cooled. It is also a very low-end and well-supported GPU, which makes this finding quite a surprise. I suspect this is due to the GeForce 8400GS never being clocked lower when idling (compared to the NVIDIA driver that supports proper power management), and as a result the temperature is quickly spiking. For the 8400GS this is not just a few degrees, but a 29°C difference that pushes the temperature on the Nouveau driver to being dangerous at nearly 80°C while idling.
The higher-end (and actively-cooled) GeForce 9800GTX was about 10°C warmer, which is not a great surprise.