I vote for (x2) 400's
This is because of light penetration and coverage.
You can hang em low and this will work well for the overall yield.
The area where the two 400's overlap light output will be at least equivalent if not greater than one 600.
I might even add some supplemental lighting from the sides, like some T5's or someting mon.
Also the 400's could be used later in a veg/mother room when you move up to 1000's.:smiley_joint:
Good luck in whatever you decide to do.:character0110:
Peace and positive vibes.
FYI - Personally I use 1000's only now.
Tried the 400, 600, 250, Str8 flouros, growzilla (2 600's in one hood), and now im VERY satisfied with my 1000.