I'm doing a small cfl grow, from what I've learned it doesn't matter what watt bulbs you could get a plant to grow under a single 40watt but yield will be small, for me I'm going to use 4x 20watt 2700k no veg stage it cost me $18 for 6 20 watt globes in a pack or about $15 for a single 40 watt you can spend up to $60 on the 130 watt globes but if your broke you can get the same power from 4 smaller globes or even more you just get "y" adapters and screw 2 y adapters info a single y adapter and a single socket will give you 4 bulb slots , y adapters go for about $2 ea on eBay , basically you want more bud get more lights of higher watts
Allot of people run say 4 cool daylight and 2 warm then switch to 4 warm 2 cool , checkout the link in daleks signature also growweedeasy and look at the training section especially if your going with a single light