From what ive seen in my own studies: You might get away with that for vegging for a while, but you will definitely want more light for the budding cycle. If you're going with CFLs, get a lot more 'warm white' ones for flowering, they will help the yield a bit. If you can, spring for an HID for the flower stage, even a low wattage metal halide will help out since you really cant give them too much light during the flowering -esp with 4 plants.

What size pots do you have them in, and are you going to veg long, or go for a short/early harvest? also big factors in end yield...