I dont see the draw for these... 2 5870's will give you the same/similar Mh for about 450 bucks
I'm thinking 6870's are the best buy at the moment. You can score them for $189 on sale and get ~300 Mhash/sec.
5830s retail for $109 (when they are in stock, which, they aren't right now) and can get easily get 280+ MH/s. I'm actually selling a pair of brand new 5830s right now (never used, as I don't mine):
http://forum.bitcoin.org/index.php?topic=21252.0/shameless plug