It's a whole lotta card, but I'm told there are issues with windowed mode and such thanks to it being native crossfire. Likewise it could be that the extra outputs only perform well for 2-D ("desktop mode") tasks. I haven't tested this and haven't seen much on it around here. If you find anything out, please share.

For high-performance graphics cards, there's a certain baseline heat/power cost just to run the thing even if it's running a screen saver. I suspect this is more efficient than two discrete cards, and certainly more so than four in a similar power bracket (you could possibly run several low-power cards for the additional monitors more cheaply). I think it's certainly an option worth looking at. Even the 4870x2 pops up for ~$400ish lately.