Some quick benchmarks were done on Tuesday at Phoronix of the Linux 3.9, 3.10, 3.11, and 3.12 Git kernels from an ASUS Ultrabook bearing an Intel Core i3 3217U CPU with HD 4000 graphics. Xubuntu 13.10 was in use when changing out the kernels from the Ubuntu mainline PPA. Mesa 9.3-devel was in use.
These early Intel Ivy Bridge Linux 3.12 kernel benchmarks can be found on OpenBenchmarking.org via 1309185-SO-INTELIVYB44. Similar to the Iris Pro results, there really isn't much change out of the Linux 3.12 kernel. For this generation-old Intel graphics core, the Linux 3.12 kernel didn't really lead to the OpenGL frame-rates in any of the games tested to be substantially different -- for better or worse.
Testing will continue, but so far the Linux 3.12 kernel doesn't appear to bring any significant performance changes on the graphics side for Intel users. At least though Linux 3.12 has a whole lot of new features.