I use 350 watts of various sizes (from 28 watt, a few 45's a few 55's a 65 etc) scattered around semi strategically in a 1.5 x 1.5 box.. If I were you I would shoot for 400 watts in that space, with some of the big ones up top, smaller ones around the sides etc.
one thing you don't need to do is have all that running at once.. you add lights as your grow get's bigger.. Start with one CFL and keep adding as your grow requires.. The ONE way to milk some efficiency out of the darn things.