Hello,
I see a price drop and could buy two 5770 cards and cf them, Would be a good thing to do instead of buying one 5850. Aslo what could of psu are we talking.
In terms of performance, 5770s in CrossFire would perform similarly to a 5870.So I would suggest that you go for the 5770 if they are cheaper.A good 650W PSU is the minimum for running two of these in CrossFire.