400 in my situation at the momnet under north star reflector in cool tube covering exactly 75x75 cm in my room or max 90cm in grow tent (more reflective)will be the best and pushing it I think
I would highly recomment go for 3x3 with 600 or 4x4 in tent
Am starting now two tents for flowering
1 secret garden 150cmx90 planing on having 1 x 600 plus 1x400 cool tubes 125mm
And one secret jarden 240x120 with 2 x 600w in 150 cool tube and maybe add one more in the future
All the best
Bubble