My reply to another post found here.

Video Card: Ok, here is where I really hope you heed my advice. The 4870x2 is cool and all, but it scales horribly. If you look at these benchmarks you will see that 2x 4870x2 cards actually perform no better than 2x 4870 cards, or a single 4870x2 for that matter. So thats an extra $489.99 for ZERO benefit it you run them crossfire. Since you are looking to go multi(3+) monitor output, I suggest going with TWO 4870 cards. This way you can enable crossfire when you want to play games on one screen, and get the same performance as your 4870x2 card. Then when you want to multibox you can disable crossfire, and run on all three monitors. I strongly recommend going with 2x 4870's. $200 each. Thats $400 for both cards. Save $89.99 and gain up to 4 monitor output while maintaining the EXACT same performance as both a single and dual 4870x2's.