so you have a separate veg room? then if you have plants that can flower in 2 months, you will get that yield.
I've seen nearly a pound off one 400w bulb, from a good scrog.
If I had a 400w I'd probably just grow two plants really bushy, via topping and lst, maybe scrog, or maybe a vertical scrog with 4-5 plants around the light
who knows what you would yield, anywhere 5-10oz