growroom size & light watage

here is a link to a chart that shows room size & the right watt bulb for your grow room. Grow Light systems Tutorial from 4hydroponics.com by Growco Indoor Garden Supply

the problem with those is that they are not meant for weed, i mean shit a 1000 is not going to cover 8x8, i mean shit 4x4 with a 600 is pushing it and that says 6.5x6.5 for a 600, a much better way is to go with 50 watts per square foot, so with that formula you will see that a 3.5x3.5 aprox is good for a 600 and a 4x4 is about all you want to really cover with it

What size room do you think is needed for 800 3 to 5 foot plants and how many watts of light?