To get 1 gram per Watt on 120 x 120 cm you do not need to SOG in such amounts.
It can be done also with less plants.
Just will take a bit more time to veg (or a little longer before you transpant your clones), but not that much.
If you would put 25 on that space I wonder how much longer it would take.
I knew guys in the past who did a lot of plants on a square meter: 100.
They had a 600 Watt HPS and had about 650/700 grams. So about 1.15 gram per Watt.
But they had a lot of work yielding them and they payed a lot for the clones.
They ran it as a test, so it was more for fun.
With CO2 you would get more, but it would mean that you also have to adjust other things in your tent.
Like how will you control the heat then?