5970 vs 6970 for 5760x1080 budget eyefinity

I've just bought 2 more 1080p monitors and i'm looking around for some more grunt to run them. I can get a 5970 for about nz$400 - 500 or a 6970 for 450 - 550.
what is the performance of these two cards in eyefinity? I'm more than happy to run with aa and af off.
the 5970 I think has more grunt but I've heard a few comments that it doesn't do very well in eyefinity for some reason...
also I could go crossfire however I don't have a crossfire board which would be another nz$167

what would you recommend? I'm happy to take other suggestions obviously but I think those are the two best options for me, could be wrong so suggest away

currently I have
x4 965be @ 3.7
8gb ddr3
5770