why 2 600s for mixed spectrum? they have dual arc bulbs, essentially 2 bulbs in one. I use a 1000w Dual arc and its basically a 400wmh on top of a 600w hps in the same bulb, looks badass when it lights up and goes a real good job. 1000w is the standard size but a few companies offer a 600w and 400w version, might take a bit of searching, i manage a hydro store and the lower wattage dual arc bulbs are always back ordered.
2 bulbs would mean more heat and twice the yearly expenses of replacing them, id stick to one bulb in the center in that tent but if you really wanted to do it.... id stack them instead of side by side, 2 side by side cool tubes in a 4x4 would leave not that much room on the sides for plants, stacked would give you better spread but it wouldnt really be mixing spectrums.
