Today I gave a try to the latest release candidate for the xorg-server and, for now, I'm feeling quite happy with it. There's been an important improvement in performance!
Using libdrm 2.4.20, mesa 7.8.1 and xorg-server 188.8.131.521 (RC1) works fine although I must set up some keyboard things to make it work properly.
Issues? Well, the xserver doesn't set the resolution of my external monitor right and leaves it to the LVDS 1280x800 which is a bit annoying as I have to change it every time I login to my computer (although I don't do it that much as I happen to be on almost always...)
I also tried the latest xf86-video-intel from git but there are stability issues: the computer just hangs after a few minutes of using the X window system. However, the performance boosts even higher with this driver!
I'm really looking forward for the next 2.12 Intel's driver release :D