I did 10 clones in appx 2 gallon containers at once, ended up pulling almost 12 ounces.
I did alot of plant rotation, every day or two. I think that was key in having a good harvest.
I tried growing a couple monster plants at once but was disappointed in the yield (5 - 6 oz). I'm going to start going in the SOG direction from here on out.
Right now I'm running 7 plants in the flower room and they are in their 4th week and I'm liking the bud production so far. I'm setting up to go 12 plants next cycle maybe as many as 20, took alot of extra clones this last round.
I think a 400w doesn't penetrate well so bigger plants won't produce much on the lower half. I think crowd them in and concentrate on getting as many buds on the canopy as possible is the way to go with a 400w lamp.
I usually take clones about a week before my plants go to flower. It takes appx 2 - 3 weeks in the bubbler for them all to root and then they veg till the next flower cycle, so about 6 - 7 weeks in veg under 4 40w T12s, so they don't get huge by any means.
I'm by no means an expert, these are just my observations over the last year of growing. So take my words with a grain of salt.