a 4890 in CF beats a gtx 295 by a fair little bit in just about every single game, so I would assume that it would be better then a 5870. In my opinion if you have a 4890 already it would make more sense to drop 200 dollars in another one, oppose to buying a 5870 for 390 + tax.
Yes but with the 5870 you get eyefinity and Dx11. I have been trying to get SoftTH to work with my 4890 thus far and zero luck. Wish ATI would release a patch that allows 4890's to do same as eyefinity.
I have a 4890 but my psu isnt made for crossfire. To buy a second 4890 ($220) + PSU ($125), I am looking at about $350 without eyefinity or Dx11. Also, the scores we are seeing for the 5870 are with immature drivers.
If I didnt have to upgrade my power supply, I would get the second 4890 in a second, but alas, i have no choice. Also can't get SofTH to work no matter what for some reason.