As I have to send back the System76 Galago UltraPro this week, which is my only system with Iris Pro graphics, I ran some last minute tests of Mesa Git master as of Sunday, 20 October. The benchmarks compared Git master to the 9.2 branch with Mesa 9.2.2 having just been tagged days ago.
Mesa 10.0 is due for release in November with a whole lot changes, including as of last week there is now Intel OpenGL 3.3 support in Mesa.
The Iris Pro 5200 benchmarks on the Galago UltraPro between Mesa 9.2.2 and 10.0-devel Git are on OpenBenchmarking.org within 1310202-SO-INTELIRIS07. You can run your own side-by-side performance comparison with the Phoronix Test Suite by running phoronix-test-suite benchmark 1310202-SO-INTELIRIS07.
Overall, there are some Intel Haswell Iris Pro gains to find with this upcoming Mesa OpenGL driver release but also some regressions; embedded below is just a sampler of the results from Kubuntu 13.10.