I've never heard of NorthQ before but looking them up it seems to be a fairly decent brand. So it might be ok for 2 HD5850 but you are probably pushing it a bit which isn't really a good idea.
The only differences between the cards of various brands is the cooler and warranty. I would mainly decide based on which is the best deal.
The Radeon 5850 will be great for your need for the most part.
If your motherboard supports CrossFire, Then instead get the two 5770
Two 5770 in CrossFire will out perform 5850 for the same price and will perform on-par or better than $400 5870
2 5770 will be around $320-330
Otherwise, If your motherboard don't support CrossFire, 5850 is still a great choice
Though a 5770 is really enough power to max out crysis, a 5850 would be cool. 600 watts or so would crossfire the 5770's if your mobo allows it, and 2 5770's is 50% better than a single 5850 for the same price. For double future proof though, get the Sapphire 5850. Sapphire always has better cards.