in my case it's error message in dmesg output only, performance is pretty the
same.

kernel ver.     3.13 vs 12.8
lightsmark    245,42    245,84
unigine:
valley        17,55    17,5
sanctuary    65,64    65,63
gputest:
plot3D        16603    16555
furmark        1519    1520
triangle    96610    96541
pix. piano    127    127
pix. volplosion    1060    1060

powered by pts :)

hardware: i5-4670 + 8GB + radeon hd7770 + display@1680x1050
software: archlinux 64b/mesa-git-00c6720/llvm-svn-199943/ddx&glamor-8 days
old/xserver-1.15/gnome3