You have the same area as I do. The answer is simple. More plants in a sea of green will net you more weight. I know your conditions and there are better ways to grow with less plants but, due to your grow room dimensions, you have to optimize.
This is my thought:
Since vertical lighting yields more weight due to better light distribution I would say go with 1 1000 watt in the middle (using cool tubes) of the room and a few lower hps or alternative lighting in the 4 corners. Grow 6 huge plants in 20 gal. DWC units around the 1000 watt and you could get fantastic results using only 6 plants. I know of a post on this site that has a vertical lighting set up with 20 gal. DWC res. and the results with 4 plants is awesome. This is 1 way around having a lot of plants and netting a lot of bud.
However,
This vertical lighting set-up requires a more square or "boxlike" room. Your room, similar to mine, is a rectangle and thus needs overhead lighting to maximize yield. So smaller plants over a larger, even surface area results in more bud.
I hope this makes sense.:thumbsup: