I'm actually surprised he would say that considering he has an Xfire setup?
yeah and I definitely regret going CF. If I knew better I would have gotten a faster CPU, an E8400 for that money and would have gotten a much better increase in performance @ 1680x1050.
At this level, E8400+4850 > E2180OC+4850CF, period. I've seen, heard and tasted both setups.
OP has a nice CPU and a nice card, and is more than enough for that res.
If another person started a thread and asking to spec him/her a graphics card for a 1680x1050 res gaming, everyone would jump in and say 4850/4870 or equivalent would be more than sufficient. Turn the question around, the OP is actually asking "would I need a 4870x2 or a 4870CF for 1680x1050?"
Clearly the majority of the answer would be a solid "no".