In ending, here is a look at the system power consumption over the course of all the graphics processors that were tested on their open-source drivers with the average / peak / low numbers.
Overall the Intel Core i7 3770K "Ivy Bridge" HD 4000 graphics performance was very competitive with its Mesa DRI driver compared to the tested AMD Radeon and NVIDIA GeForce hardware on their open-source Gallium3D drivers. With the proprietary cross-platform AMD and NVIDIA drivers, the performance (and OpenGL support) is obviously much better overall and both drivers have proper management, but when it comes to those interested in open-source GPU drivers, Intel is largely leading now with Ivy Bridge. Sandy Bridge was already great for the very light gaming or someone just wanting a composited GNOME/KDE/Unity desktop for office, Internet, and other basic Linux desktop needs. With Ivy Bridge, the Intel open-source Linux offering has become much more interesting and competitive. Besides very good performance and power efficiency compared to the discrete Radeon and GeForce graphics cards on open-source drivers, the open-source Intel Linux driver does offer VA-API video encode/decode acceleration. Intel's VA-API is implemented with their video engine unlike the Nouveau/Radeon Gallium3D drivers that are doing VDPAU/VA-API with GPU shaders over Gallium3D.
In a few benchmarks (such as Doom 3 and Xonotic) with high quality effects and lots of GLSL usage the Intel Mesa driver fell behind with the HD 4000 graphics, but hopefully with the ongoing OpenGL/GLSL work being done by Intel OTC developers this will improve with time as they gain better OpenGL conformance. For many of the Linux OpenGL benchmarks when comparing the graphics processors on open-source drivers, the Intel i7-3770K Ivy Bridge was competitive with the GeForce 9800GT and Radeon HD 6570/6770. It's also important to note that the Nouveau/Radeon drivers were forced to their non-default optimized states: the Radeon driver had PCI-E 2.0 support enabled (by default it's still capped at PCI-E 1.0 speeds for Radeon GPUs...), 2D color tiling (not yet enabled by default), and manually disabling swap buffers wait. For the NVIDIA GeForce hardware with the Nouveau driver the GPUs had to be manually re-clocked to their highest operating states. Had the Radeon and Nouveau drivers been tested in their true "out of the box" states like the Intel driver, the Ivy Bridge graphics would have likely overruled these eight PCI Express graphics cards tested today.
A larger comparison involving more graphics cards and the high-performance AMD/NVIDIA drivers is in the works for the coming weeks. In the meantime you can see other recent Linux GPU driver benchmarks from the results within AMD To Drop Radeon HD 2000/3000/4000 Catalyst Support, Open-Source NVIDIA Driver Approaches Stable State, A 14-Way Comparison Of NVIDIA vs. Nouveau Drivers, and The Most Comprehensive AMD Radeon Linux Graphics Comparison. Other Intel Ivy Bridge Linux benchmarks are also on the way.