Lowering your memory clock can also decrease your core temps a couple to few C. 

Increase the fan speed a few %?  Can work wonders.  On my 6870 I took fan speed up 5% from auto settings and it decreased my temps 6C.

Isn't the -f setting in GUIminer allow for more or less desktop usage?  Still mine at 100% but allows other apps to utilize some gpu power if needed.