Clock-For-Clock, Nouveau Can Compete With NVIDIA's Driver
World of Padman also faired well for Nouveau when comparing the clock-for-clock performance between the two NVIDIA Linux drivers, but still it's the Nouveau driver that is handicapped by not being able to run the hardware at its rated frequencies. The Nouveau driver also doesn't support the greater OpenGL (3.0+) levels handled by the NVIDIA proprietary driver and lacks features like SLI and VDPAU with PureVideo HD.
With the more demanding Reaction Quake 3 open-source game, when both drivers were controlling the GeForce 9 graphics cards at the boot frequencies, the NVIDIA proprietary driver carried the advantage.
Clock-for-clock, with the very basic and not-demanding Tremulous first person shooter, the Nouveau driver was faster at the reduced clock frequencies.