For some fun Thanksgiving Day benchmarks, here are numbers of Mesa 12.0 vs. 13.0 vs. 13.1-devel Git on an Intel Core i5 6600K "Skylake" system with HD Graphics 530.
All other settings/hardware was maintained during testing aside from swapping out the Mesa build.
While for many tests the Intel OpenGL performance didn't change much since Mesa 12.0, with the Mesa 12 release there was just OpenGL 4.3 support while with Mesa 13.0 and newer is OpenGL 4.5. Also in this time the OpenGL driver has somewhat taken a back-seat to the many optimizations and continued work going to mature their Intel Vulkan Linux driver. Fresh tests of that shortly -- to complement yesterday's Intel Skylake OpenGL vs. Vulkan Numbers With The Latest ANV Mesa Changes.
Unigine Valley is one of the few tests to show a noticeable performance improvement with Mesa 13.1-devel on Intel Skylake hardware.
While the other results aren't too exciting, you can see more data via this OpenBenchmarking.org result file.