You shouldn't have an issue.  Do you own a Kill-a-watt unit (http://www.newegg.com/Product/Product.aspx?Item=N82E16882715001)?  If not I would suggest purchasing one.  It makes tweaking your system to draw less power much easier.

I have 3 x unlocked 6950's generating 1050 Mhash/sec and the whole system is drawing 460w.