Phoronix benchmarks have already shown how already for the Haswell CPUs less than one month old the Linux support has evolved a lot and extensively benchmarking the Intel HD Graphics 4600 on Ubuntu from the Intel Core i7 4770K.
With the latest Mesa Git code being trivial to obtain and the Phoronix Test Suite being so easy to use to carry out tests in an automated and reproducible manner, I ran some more Mesa 9.1 Git branch versus Mesa (9.2-devel) Git master benchmarks on Thursday evening from my Haswell desktop system.
This testing was from an Ubuntu 13.10 installation with upgrades to the Linux 3.10 development kernel and playing with Mesa from source. As this is just a benchmarking quickie, the results in full can be found on OpenBenchmarking.org via 1306217-SO-MESA92UPD63. With the Phoronix Test Suite, you can also compare your own system's performance against today's results by simply running phoronix-test-suite benchmark 1306217-SO-MESA92UPD63.
As already written about at length, when upgrading to Mesa 9.2 there are some major performance wins for Intel Haswell graphics on Linux.
Mesa 9.2 will be officially released around September or October of this year. Beyond delivering better performance for Haswell, it also will deliver better OpenGL coverage (hopefully in compliance with OpenGL 3.2~3.3) and other new functionality.
View more of these Mesa 9.1 vs. 9.2 test results in its OpenBenchmarking.org result file.