CFL's can produce around 60 lumens per watt. A good 600W will produce 160 lumens per watt...

For excellent flowering growth you want 5000+ lumens per square foot. It's going to be pretty hard to get that at all with CFL's. Don't get me wrong, i've seen good CFL grows before, but the BEST grows i've ever seen are with HPS or something similar.

If your grow is 4'x4' or bigger, def get a HPS. If it's more like 2'x2' or 2'x3', CFL's would probably be more practical.