Chris Wilson of Intel's Open-Source Technology center continues releasing frequent Intel X.Org driver updates. The performance tuning for the Haswell GT3/GT3e graphics cores comes down to setting proper thread counts for the GPU and handling some scaling issues with the embedded DRAM.
This driver also includes a fix for a "critical issue" with Gen4/Gen5 Intel systems that was causing some issues. There's also a crash fix for Planetary Annihilation and triple buffering is now disabled for compositors.
Chris Wilson made 43 changes to the xf86-video-intel driver for the 2.21.14 release in the past week. The full list of changes can be found on xorg-announce.