I think if it were me, I would close off the veg and clone areas and leave the large space open for flowering. That way you would get some overlay in your lighting. But I would probably run led too, so we would already be planning in different directions.
As far as yeild, you’re right. Too many variables to guess. Experienced growers claim a gram per watt on 600’s with right strain and methods. But I’ve also seen very good growers struggle to get .5 per watt.