I upgraded the AMD Catalyst 12.8 to 14.6 beta on my Debian Squeeze 32 bit mining rig. I then compiled djm34's modified sgminer, here are the results.
On 12.8 (sgminer by lasybear):
GPU 0: 41.0C 0% | 2.323M/2.323Mh/s | A:293 R: 1.7% HW:0 WU:0.033/m I:20
GPU 1: 46.0C 0% | 2.278M/2.275Mh/s | A:290 R: 2.0% HW:0 WU:0.033/m I:20
GPU 2: 41.0C 0% | 2.262M/2.262Mh/s | A:263 R: 1.5% HW:0 WU:0.031/m I:20
On 14.6 beta (sgminer by djm34):
GPU 0: 41.0C 0% | 3.359M/3.349Mh/s | A:19 R: 0.0% HW:0 WU:0.039/m I:20
GPU 1: 45.0C 0% | 3.357M/3.343Mh/s | A:15 R: 0.0% HW:0 WU:0.031/m I:20
GPU 2: 40.0C 0% | 3.326M/3.344Mh/s | A:27 R: 0.0% HW:0 WU:0.070/m I:20
More than 1 MH/s hashrate increase per HD 7950 @ 975/1475 for X11.
Remember to delete /etc/X11/xorg.conf and regenerate it with "aticonfig --initial --adapter=all" and remove the existing .bin files that the other sgminer version generated (segfaults).