well. 150w is supposed to be good for 4 plants in a 2x2 area = 4sqft .. marginally a 3x2 area = 6sqft
so double that = 300w you could get 8 plants with that many lights.. 400w means you could probably comfortable get 10 plants
the size of the area DOES matter though. even with 400w if your area is too big its pointless.. cfls have to be close to be effective. 8x2 = 16sqft... that may be TOO big.. but keep the lights close and you shouldnt need that much space. ..