Coverage isn't the only determining factor my friend, useable light.. remember, you mentioned yourself, the par watt conversion for LED? Coverage area is not an efficient measurement of the strength of the light. I use a 600W HPS in a 2x3 space and the plants at the edge of the canopy don't thrive quite as much as those in the middle. No one is saying the plant won't grow with the LED, we're saying that it won't grow as well. Also, note he said "800W of HPS" from 2.. not 600W of HPS from one.. so, that's 400W HPS each and 2x3 is about right for a 400W HPS good sir. That's 75W/sqft.