Self answer:
DJDAFIDAK was right but did not say 'how'.
So here goes ... HD 6850 to HD 7850 (ASUS 7850 2 GB)
1. Go to AMD website. Find the new driver for "AMD 7xxx"
2. At the bottom of the screen list is a program, "AMD uninstall program". I ran this PRIOR to physically putting in the new card. Apparently if you just windows uninstall catalyst there are still traces of catalyst that can affect your new card. Some folks have had trouble with the AMD uninstall program (not win 8 friendly? ). I ran it in win 7 - no problems noted.
3. Physically install new card. ASUS hd 7850 2GB is long folks. very long ! only about 1/4" to spare in the CM HAF 912 !!
4. Power up machine.
5. Fresh install of Catalyst 13.4 (i believe)
Smooth as silk !!
Good Luck !!