i need help

Two 5770's in CF will work out most likely cheaper than a single 5870 but you honestly can't beat the sheer performance of the 5870. The rule of thumb i always tend to stick to is never CF or SLI two cards if you also have the option for getting a single more powerful one. I always think CF and SLI should be reserved for the top end cards.

Anyway, my advice is, spend the extra money on a single 5870, either way you're gonna blitz Crysis at 1080 anways...

That is my reasoning as well. And although it is improving, there will always be some inconsistency in SLI/Crossfire compared to their single card counterparts.