7870 will give a better gaming experience. crossfire is stuttery in general and with mid range cards like 6870's makes it even worse, not to mention they are 1gb cards vs the 2gb vram on the 7870 which will help in all new games which are mostly using 1gb vram+ now. I used to run 2 6850's in crossfire and a couple months ago switched to the single gtx660 and its much smoother, even if benchmarks swing in the way of crossfire 6850's, the experience was not smooth. Much better off with a single better video card. I would tell you also to consider the gtx660, its is comparable to the 7870.