I know this thread is a few months old but figures I'd chime in. inregards whether it's better to run 2 - 315w cmh vs 630fixture. I've found that in any tent grow 5x5 or 4x4. it's really better to run the 630w dual bulb fixtures instead of 2 fixtures. reason being having the 315w. bulb In there own hood, create a good amount of par. but the intensity really is limited. with a foot print of 3x3. having 2 fixtures inside a 4x4 or 5x5 is really just hurting your intensity. yeah penetration is a tad better, but again only because or different angles of lighting. the 630w cmh are more intense than a 600w hps and penetrate better. its covers up to a 5x5 footprint. packing two 315w bulbs under the same hood creates a very intense light that covers the entire tent area. so why sacrafice that much better penetration for better spread in an areawhere your already completely covering it with a 630. I yielded 700 grams in a 5x5 with only 6 plants and having the tent two thirds full . easily over a gram per watt and wasnt even scrogging either