In recent days there have been updated Mesa 8.1 development benchmarks put out looking at the R600 Gallium3D, R300 Gallium3D, and Nouveau Gallium3D open-source drivers. Those results for the different drivers show that Mesa 8.1 is generally faster than the current Mesa 8.0 stable series, but that does not appear to be the case for Intel at the moment. It looks like there are some active regressions that are lowering the Intel Ivy Bridge graphics performance with their Mesa 8.1-devel driver.
In this article are some Intel HD 4000 "Ivy Bridge" graphics benchmarks from an Intel Core i7 3770K processor. Testing happened on the same setup as the other recent Mesa 8.1-devel benchmarking and with the same software: Ubuntu 12.10 with the Unity 6.0 desktop, Linux 3.5 kernel, etc.
The Mesa 8.0.4 to Mesa 8.1-devel performance is being compared in this very straightforward testing.