First up with Nexuiz, we see the open-source R600 Radeon Gallium3D driver for HD 5000/6000 series graphics cards is generally the better part of 50% the speed of the Catalyst Linux driver. The Radeon HD 6870 performance was surprisingly at 82% the speed of the binary blob.
The Radeon HD 7000 series performance is quite poor for now as its Radeon Gallium3D driver is still being brought up but its performance will also improve on the Linux 3.11 kernel due to dynamic power management / re-clocking.
The open-source NVIDIA driver (Nouveau) performance continues to be quite slow too, in large part as well due to re-clocking. Unfortunately, there's still no mainline re-clocking support for the NVIDIA Fermi / Kepler (GeForce 400/500/600/700) GPUs with the open-source Nouveau driver.
The Intel HD Graphics 4600 "Haswell" performance was faster than the Radeon HD 4650 GPU on both its open and closed drivers. Due to the Nouveau re-clocking performance problems, it also outperformed all of the NVIDIA GPUs tested on the reverse-engineered open-source driver.