My recommendation for that much light:

8x8 space
one light over every 4x4 (gives 25W/sq foot which is a bit low but will work)
SCROG the entire area with one plant per 4x4 square.

It will take some time to fill the screen this way, and if you are in a hurry and don't mind the plant numbers you could do 2 plants per 4x4 space.

With a decent strain you would pull 2lbs+.

I would expect about 4lbs, but that is with a heavy yielder and I know a little bit about the process.

I hope that helps. I really hate to have a lot of plants.
Bachelorpads Reviewed by Bachelorpads on . 4 x 400watt HPS's How many plant can i fit under 4 x 400watt HPS's is i only veg the plants for 2 weeks and how much room will i need? Thanks. Rating: 5