Unfortunately we still don't have any Iris Pro 5200 benchmarks on Phoronix due to simply not yet having any GT3e hardware, but Daniel Vetter has written on his blog about the Linux 3.12 i915 DRM changes and with that he notes the GT3e hardware has the eLLC cache enabled.
Ben Widawsky enabled the giant eLLC cache while Chris Wilson enabled a write-through scanout buffer-caching mode that benefits hardware with this embedded DRAM package.
Other Intel graphics changes for the Linux 3.12 kernel include enabling PC8+ support as a deeper system sleep state for Haswell ULT platforms, Panel Self Refresh (PSR) support is now in place as another Haswell power-saving feature, and an assortment of other improvements.
Some of the smaller work includes GPU error state reporting via sysfs, HDMI infoframe changes, Fastboot support, and VMA object support for GEM.
More information on the Intel DRM driver changes queued up for merging into the Linux 3.12 kernel as soon as Linux 3.11 has been released can be found on Daniel's blog. You can also read about other great features for the Linux 3.12 kernel on top of the Linux 3.11 features.