Switching from 400 watt to 600 watt

So let's say you have 6 plants under a 400 watt hps. Let's say each plant yields an ounce under the 400 watt. If you were to switch the light to a 600 watt hps, about how much would this increase the yield by?

under the exact same conditions the increase in yield would be nil. you'd have to veg longer or flower more plants to see the benefits. high density sea of green is what you want