Well, before jumping to the results, first here is a look at the system power consumption while idling with each of the graphics processors. The Intel Z77-based system with the Intel Core i7 3770K using the integrated HD 4000 graphics was going through 40 Watts on average while idling, the Radeon HD 4670 at 766 Watts, the Radeon HD 5750 was at 89 Watts, the Radeon HD 6450 at 51 Watts, the Radeon HD 6570 at 71 Watts, and the Radeon HD 6770 at 106 Watts. On the NVIDIA side, with the NVIDIA GeForce 9500GT installed the system was burning through 58 Watts at idle and 54 Watts for the GeForce GT 220. Compared to the Intel Core i7 3770K, the Radeon GPU consuming the least amount of power was the Radeon HD 6450 with 52 Watts for total power consumption (+30% more power than idling with just HD 4000 graphics) and 54 Watts on the NVIDIA side for the GeForce GT 220 (+35%).
The first graphics tests for this open-source Mesa/Gallium3D driver comparison was running Nexuiz at 1920 x 1080 with HDR enabled. The Nouveau graphics cards could not be tested since with this driver and Ubuntu 12.04's X.Org Server, Nexuiz does not run. With this Nexuiz run, the Intel Ivy Bridge HD 4000 graphics performance is comparable to the Radeon HD 4670, Radeon HD 5750, and Radeon HD 6770. There appears to be some Radeon driver bottleneck with those three graphics cards being of different generations and capabilities but all running at around the same level for this DarkPlaces-based game. Even so, with the tweaked Radeon configuration (disabling swap buffers wait, enabling PCI-E 2.0, and enabling 2D color tiling) it took these higher-end Radeon HD graphics cards on AMD's open-source driver in order to compete with Intel's open-source driver and their latest integrated graphics. Intel's also using a classic Mesa DRI driver still rather than Gallium3D, which many commonly misreference as automatically making for faster performance. The Radeon HD 6450 and Radeon HD 6570 with Radeon Gallium3D sharply lost out to the i7-3770K graphics.
While the HD 4670/5750/6770 graphics cards performed close to the Ivy Bridge frame-rates in Nexuiz, when factoring it out to performance-per-Watt, the Ivy Bridge graphics processor has no competition. The HD 4000 graphics core when comparing open-source drivers was offering 48% better performance-per-Watt than the leading AMD Radeon graphics card on its R600g driver. The worst performance-per-Watt was actually with the low-end Radeon HD 6450 graphics card on Gallium3D with the Ivy Bridge graphics being more than twice as efficient.
The Intel Core i7 3770K with the Nexuiz load was leading to the system needing 72 Watts while the Radeon HD 6450 needed just 62 Watts (but with very disappointing performance) and the Radeon HD 4560 needing 96 Watts. The most power-hungry GPU tested was the Radeon HD 6770 at 125 Watts. The open-source Nouveau and Radeon drivers still lack good power management support.