Wait, I'm confused -- you have these flowering under one 400w, yes? As an example, if you were to just use the .5 GPW number for horizontal I mentioned above (and again, that would really be a shot in the dark, but if you did) you could roughly plan on around a half pound of dried and manicured flowers come harvest time. If you were running a vertical, using the .7-.8 GPW number above (we'll call it .75 GPW) you could expect roughly 300g of dried and manicured bud. Again, you could get way more or way less, but I've found that coco is forgiving enough in the yield department that you're not going to be too far off with those numbers as a baseline estimate.
One other thing I should have mentioned in my post above is that would be based on a 4-5 week veg, but again, so many different variables in play from strain to strain, environment to environment, etc.
I'm a little lost on where you got the 600g number from.