I answered a lot of questions this run. I setup the 150 on one side of my tent and a pair of hanging shop lights with cfls on the other. This allowed me to keep that 150w 8" above the top of the plants over 1.5 feet. ( my tent is 3' wide.) I used 4 cfls on the other side. I'll have a pic of my setup here.
I tried a few different ways to train but basically grew 4 plants under one, 150w hps. Here's one FS c99 that I supercropped and lollipopped under the 150w. It's still growing today BTW.
I think to cover 4 square feet a 150w works just fine. It would cover more but the closer you have the light the more weight you put on per plant.
I learned you could do a lot in 4 square feet and a 150w and have no plans to upgrade.