I know 5770's are similar to the 4870, and I know 5770's (x2 xfire) are the same/a tad bit better than the 5870. I know the 5770's overclock like a champ, but considering the 4870 is a tad bit better htan the 5770 im asuming that yes, 4870's CF are better than the 5850.
sounds like a good idea plus i play a lot of dx 11 games so. as far as manufatures go, what would be the best right now i was looking at a powercolor with a stock overclock core clock of 760 mhz would sapphire or xfx be better? i around 300$ to spend so.
I like XFX better for their double lifetime warranties. I would also recommend the 5850 for better future proofing, as well as better efficiencies already mentioned. However, I am running 2 x 4890's in CF and they get better frames than a 5870.