I've got a 7850 & 7870 running in crossfire (price changes, don't ask) paired with a 1055t at 3.8ghz and at 1920x1080 it runs with everything 100% maxed out in single player at 60+ fps (average above 80). In multiplayer mode with 64 people it can drop down below 60 when stuff gets really crazy, but for the most part runs very, very well. And that's with the equivalent of 7850's crossfired, With 7870's and a strong cpu you'd do even better that that.
Note: To run crossfire, I stuck with the 12.3 drivers, after having looked around online and seen many comments suggesting that the early drivers were the best for crossfired 7850s/7870s. The only downside to this is I have problems with some newer games, such as The Secret World is kind of buggy for me.
After a quick google, here's a review of crossfired 7870s at 1080p.
http://www.pcper.com/reviews/Graphics-Cards/MSI-R7870-HAWK-Review-and-CrossFire-Performance-AMD-HD-7870-Steriods/Result-3Edited by Dannyboy3210 - 10/4/12 at 10:36am