do all amd cards now use the same drivers as in the amd catalyst. my 4850 is currently up to date (11.9) but if i replace it with a 6870, will i have to uninstall the drivers only to install 11.9 catalyst again?
Usually no. But sometimes issues do into play so it's still suggested you uninstall the driver, put the new video card and then install Catalyst again.
And yes, most of their video cards can run on the same Catalayst drivers, except the really old ones.