im using a 600 watt for 6 plants, they love it. 2x6x8 closet. mixed genetics, 3 dwarf plants(no taller than 24 inches lots of bud filled branches.2 indica's that have reached 42 and 46 inches.1 pure Jamaican sativa*lamb's bread* only time will tell on that ones height.

if you grow heavy yielding lowryder plants(20-25 inches. looks like a giant nugget-no long branches just buds) you can probably get away with 8 to 12 on that setup