You are a bit more sophisticated than some of us, lol....
I just go by the 50 watts of HID per square foot, and use the best bulbs I can find to squeeze out a couple more lumens.
I'm happily running 1400w HPS in a 5x6 space.

Your issue is going to be DISTRIBUTION, since you want big ass honkin' bitches. If I wanted to grow that style, I would switch to 4 vertical-burning HPS600s in parabolic reflectors. ATM my plants are under a single 1000 and a 400 (when they first enter the flower room), and they have to be bent over short to take advantage of the light. With multiple points of light, you get the luxury of side lighting to your big bushes.
Just some thoughts. I think BlueBear- who was growing BIG plants- was running parabolics.