Before you shell out on the 7950GX2 (s) may i ask what LCD you're looking at right now?
For a 19" LCD a single 7950GX2 is (massive) overkill. The most you need to run at that resolution with (nearly) all the eye candy is around a 7900GT. Going to a 7900GTX or the GX2 gives you more fps, but with a few exceptions the 7900GT gives playable fps.
For 20" widescreen to 24" a single 7950GX2 is more than good enough, especially if you overclock, a slightly higher end options may be X1900XTX crossfire (especially if you go for water cooling). If you're talking 30" LCD then i'm going to go sulk because of the unfairness of it all :|