SLI or CROSSFIRE dual GFX card solutions have been debated many times over. It very well could be a waste of money. But, to each his own. Bragging rights or no bragging rights... Whatever.
One thing I do know is this. If you want to run a "new" game on a 23" or 24" inch widescreen LCD monitor at their native resolutions 1920X1200 or 1600X1200 and you want to crank all of the video settings to maximum, you dman well better have an FX-57 and (2)7800's or (2)X1800XT's because (1) GFX just isn't going to do it.