is it really worth the extra money to have a multiple gpu setup? I'm running 1680x1050 res and was thinking of getting another 4870. In general, does going with multiple gpu's really make that much of a difference in gaming compared to a single card? Is the performance increase worth the 100% price increase? Would it be better to go with just a ultra powerful one card solution?
p.s. im curious about both nvidia and ati not just crossfire
I suppose it'd be worth getting if you wanted to do gameplay recordings. Other than that, just about every game performs great with the 4870 and would be unnecessary to get another one.
You'll see performance gains in some games, and you'll see performance decreases in some games. Personaly I like to stick with one card.
SLI and Crossfire is great and a necessity for high end games like Far Cry 2 and Crysis/Crysis Warhead. The best option for anyone considering this kind of setup is to keep in mind that some games don't support multiple GPU's. So have two high end cards rather then 2 moderate/low end cards, that way your games will always be at a playable framrate.
SLI/Crossfire does have limitations though. More then two GPU's (in general) scale horribly. (scaling is both an increase in performance and visually how the game will look.) The problems you may encounter with 3 or 4 gpu's is micro stutter and a phenomina known as diminishing returns, where you keep adding video power without any real gain.
Remember, the biggest determining factor in running multiple video cards is your resolution, IMHO 1600x1200 is a minimum, with 1900x1200 being the resolution to strive for and 2500+ being insane 
I was pondering the thought of getting another GPU to crossfire it with my current one, which is an HIS 3870. Will it be possible it crossfire the HIS with a Sapphire or a Visiontek?