Nice plants. I am going to hafta show these pics to a friend of mine who grows also a mmp. He won't use a hps bulb because they create to much "heat" can't convince him 600watts doesn't get hot. He uses the t5 fluoro bulbs 16 of them for a total of 864 watts of light and his plants look about half size of yours when they are finished flowering. He also thinks they get to hot tho an keeps the lights about 4 n half feet from the tops of the plants. He has the same grow hut as yours just double the size I think
Sounds as though your friend is keeping his fluoros too far away, and he also needs to get his ventilation in order. 864 watts of fluorescent light is about 51,000 lumens. 600 watts of HPS light, is 64,000
lumens, and in my experience even lumen for lumen, HPS still out-performs.
But even with his current set-up, if he could manage to keep his lights 70% - 80% lower and closer to the canopy, he'd see a marked improvement.
This may help him change his mind though, about switching light systems...
150w incandescent = 2,550 lumens or only 17 lumens per watt
150w halogen = 3000 lumens or 20 lumens per watt 150w of Fluorescents
= 9,000 lumens or 60 lumens per watt 150w of Compact Fluorescents
= 10,500 lumens or 70 lumens per watt
150w Metal Halide = 13,500 lumens or 90 lumens per watt 150w High Pressure Sodium
= 16,000 lumens or 107 lumens per watt
He should also keep in mind that, especially with more intense lighting, he can cut his temperatures down greatly just by keeping his ballast/s outside the actual grow space, in a separate but adjacent room.