According to the information from the same thread, unfortunately 11.7 and 11.8 have a bug that causes 100% cpu utilization on a core. This may be causing the loss in performance.
I am running the catalyst 11.7 pre release drivers and while my system objectively seems more stable it still crashes on youtube or vlc. But i got like.5-1 mhash/s better than with cataylist 11.6 hope that helps at all. I think the above poster is right and it will be resolved in 11.8