if you are really going to do SOG then reduce the size of pot to 15 cm or 6 inches 3.5 liters each,
The lamp is fine for 1 square meter in sog ,,you have 1.5 meters square, with only 16 plants, i imagine you want to grow your crop a little bigger than in sog, there fore the penetration of a 600 watter would be much better,,
the 600 hps unit , is the most efficient of all the lamps when comparing lumens to power output!there for always better a 600 than a 400.
whowever i have two meters square that share three 400 lamps and another two square meters under one 600 each, although it is cheaper to run two 600's the three four hundreds give a better light dispersal over that area. of course the more light you have the better!, unfortunately this cost has to balance with the value of the crop! and the electricity bills have to be,,,,,,"reasonable" so as not to attract too much attention from the electricity supplier!.
by maintaining the crops under two feet high when finnished ensures good light penetration and the need for more powerfull and costly lamps to run, combine this with 36 plants per meter square, and you have 350 to 400 grams under a 400 watt hps, no probs, each plant only has to produce ten grams of dry bud to make 360 grams! the idea is to maintain the plants on one cola![bud] again the room needed for a ten gram plant is minimal, and if you guard the plant tank from the light, the roots will grow out of the bottom of the pots into an inch of sollution that should be left in the plant tank always!, when removing the plants for cultivation the roots form a blancket over the bottom of the tank!

good luck with your grow


welcome to the world of endless possibilities,,,,,,hydroponics!