What version you're using now doesn't matter, just update to the newest available... which also should update your SDK to 2.4, some people say it reduces preformance but i personally haven't seen any of that nonsense on my 4850x2 nor my 5850...
Also you might be better off using Phoenix with phatk kernel, at least i get around 20mhash/s more with it on my 5850
Edit: also make sure the card is getting enough power and that you have a dummy plug/extra screen attacted to the card if it's a second card in your system