phaded420, I use the same size tent.
I bought 1 400watt MH/HPS under 7 plants
and found that the side plants wouldnt grow as well
as the ones in the center and as you know pulling
everyting out of the tent to reposition is alot of work.
For my sec grow I bought another 400watt MH/HPS
and started with 11 and ened up with 7 females.
This number works great I use up every inch of the tent
and with 2 400watt lites all plants have enough light.