Hps is the most efficient light known to man. so there is no savings on power

the only benefit to CFL's is that they give off little heat. so you can get a smaller vent system and you can get the lights closer to the plants.

think about this a 400W hps gives off 50 000lm's

you would need to buy 4 200W clf's (at 12 000 lm each).
So 800Watts of power. double. Not to mention that they are huge and would take up a large amount of space. AS well you will need to buy reflectors for each one, so thats like 20-30$ each.

hmm. They seem like a great idea for really small grows.