Motherboards published an ATI HD 5770 and HD 5750 Crossfire review.
Quote from the review: "Two HD 5770 cards perform better than a single HD5850 card and two HD 5850 cards perform much better than a single HD 5770 card. Considering the price of the two HD 5770s is nearly the same as a HD 5870 card I would suggest buying a single HD 5870 or HD 5850 depending on which price range.
On the other hand, if you only have $160 a HD 5770 added to the system later will improve performance immensely in most applications. Two HD 5750s in Crossfire mode make for an attractive upgrade as well if you only have $130 to spend on a video card today. "
Read the full review on Motherboards.