If I drop to 11.6 Catalyst drivers will it reduce my MHash/s? 

I have 11.8 Catalyst drivers and get good MHash/s but one core is locked full too.

Also what fan control are you guys using?  With my XFX 6870, if I leave fan control on auto, it will stay at 35% fan and let the temp get up to 84 deg C, so I manually set it at 50% to drop the temps to about 78 deg C.  What are reasonable maximum temps for 24/7 operation, and will I wear out the fans at a 50% speed 24/7?