400hps in comparison to 600hps help

I've been using two 600w hps in a about 8*3 well reflected area. I normally have between 5 - 6 fairly bushy plants white widow from greenhouse. I've been averaging 4oz per plant.

I have some extra clones and a spare 400w hps plus some room to spare. I'm wondering how many I can put under the 400w in what type of dimensions all other things being similar to match my yields under the 600's.

I'd go with 4 plants...keep them slightly more compact than under the 600 and you'll be set.