The 7900GT,7900GTX, 7950GX2 and 7950GT all have 2xDual Link DVI. So all four will run 2 30 Inches fine. However, unless your going to be gaming a ton, you would be better off with either GT or GTX than the GX2. Not to mention, when using 2 monitors I am pretty sure you can't turn on the 2nd core of the GX2. This would mean your be stuck with essentially a super expensive 7950GT. Of the four cards I mentioned, and since you already were willing to spend money for a GX2, I would go with a 7900GTX as it is the quietest of the bunch.
8 Megapixels of desktop space is kinda scary though, but in a good way.