you can do better than that....of course 50 watt per sqft is optimal level but again that would be a waste of watts....from what i've read in erowid i think (that's why i do not post the link) you can have a successful garden with 3,000 lumens per sqft....a 600watts hps emits around 90,000 lumens....that equals to 30sqft of space....the manufacturer of my 400 hps states that can cultivate in a space 4x4 ft=16sqft=25 watt/sqft.....moreover , it depends on the strain that you choose to grow....how tall and how bushy.....i agree to the thought of the way you choose to grow but the only factor that limits the amount of plants that you can grow in a certain space is their height....
also i've read this thread (report number 3) http://www.overgrow.com/strainguide/...ht/1440/#g1440 .....check how many plants can be grown from seed into a sqft........i grow the same strain into a space of 6x3 under 2x400 hps....
anyway what i want to say is that it all depends on the height of the plants...
i have 4 of that strain that cover the area of 16 sqft and 3 of the same strain in the area of 2sqft....and all of them are budding.....
the second hps was added only a week ago to enhance budding......
with the 600 hps you can grow to full maturity around from 1 (an enormous bush)to 16(small to medium plants) and maybe even more plants.....it all depends on plant size....ie i think with my 400 hps could grow 16 Lowryders in 16sqft.....1 per sqft........