Just ran the AMD update. Have 3 5850's running clocked at 900/300 1088volts and have been getting 325Mh consistently. Now....all 3 cards are running under 250Mh.
WTF?
No need to roll back the whole driver. Run the uninstaller for Opencl only, then extract your old driver and install just the old file.
Only downside (of it is one) is that further uninstalls and updates may fail to remove the old cl SDK unless you keep the original installation file.