The Grim Reefer
Ready for some NOBALL!!!
6 will get you started if 4 are overdriven. I would go with the 660 for 4 of the lamps and a standard ballast for the other 2. I think having 2 rows of overdriven Daylights or sun lamps with 4 rows of standard driven lamps will provide plenty of light unless you want to do mainly SPS.