What ghb said; Way to big of a space for CFLs you would have to spend so much money on bulbs that it would be better to go HPS/MH
also 2 - 3 plants in a 6 x 6 is a long ass veg period and huge plants to maximize yield for the space. If you really want to go CFL, you don't have to use the whole 6x6 though can just use a corner of it.
you need a mix of 2700k and 6500k color spectrum at 23watts each (most efficient lumen to watt ratio). The 6500k are about 5$ a pop, the guy above has 30 bulbs so if 15 were 6500k that's 75$ just for half his bulbs. I made a 184watt DIY CFL reflector (8x23 watt CFLs); after bulbs, power cords, ties, vent pipe, etc was only about 80$ to make I thought I was golden. Well the temps weren't as cool as people said. End of day i regret not spending the extra what 50 bucks and getting a cheap MH/HPS at 50% power (budget 400watt HPS systems start at 125$, you can run it at 200watts if power draw is a concern, but again 8 CFL is 184watt draw). So yes CFLs are cheaper to a point, are cooler to a point, and draw less power to a point. Anyone with more than 150 watt of CFLs is doing it wrong IMO you will get more with other lighting options guaranteed.
I am not knocking CFLs they are great for very small cabinet grows, seen people pull 2 zips with 4 bulbs in a cab. But a 6x6 space go LED or MH/HPS. if you are considering CFL I assume you are on budget so LED is out of question.