If I remember what I read right the 42 watt cfl's are one of the most efficient cfl's when it comes to lumens per watt. I could be wrong but its something to think about and look into further. Hope this helps and good luck with the grow.
I am growing with 6 42 watt cfl's in a rubbermaid tub right now if you want to check it out my log is in my signature.