I seriously need to get a new card - What do you guys think?

Hey guys,

I've got a twin 6600 GT leadtek that's pretty worn out.

It cant even handle FEAR in high detail without lagging on 1024 x 768.

So I'm thinking of buying a 7800 GTX 512 meg... and perhaps down the track when I need a boost in performance I'll buy another of the same card and run in Sli.

Should I go ahead and do this?
What do you guys think I should get?

Any help is REALLY appreciated.