waybaked.....what um stuck on is the length of my table wich is 7 0r 8 feet in length and 5 feet in width...6 or 7 feet from table to ceiling......ok i want to put 40 girls in 10 litre pots in that grow space...i mean all the pots will fit.....ok now im tryna get a better view on wether 3 400's would cover that space and provide at least 3 ounces per plant or will i only get that number with 2 600's???
There are a lot of variables that will make a lot more difference than the choice between 2x 600 and 3x 400.
If 3x 400W is significantly easier for you to set-up and use, then by all means do it, just use the reduced heat to bring your lights closer to your plants.
If they're about equal in difficulty of use, then go with 2x 600W because it will result in better coverage.
From the start, though, if your grow floorspace is 8' x 5' = 40 sq. ft. then 1200W will only result in 30 watts per sq. ft. A minimum of 40-50 watts per sq. ft is recommended for Cannabis. It will work, but yield can be expected to be diminished.
If your only choices are 3x 400W or 2x 600W, however, I would have 2x 600W each covering a roughly 5' x 4' area.