To answer the 'how big' question, what you see is what you get- that bud was an entire plant. It also had about a half dozen fan leves on it, but I cut them off when I harvested it.
I only use the HPS in flower. The confusion over mothers under HPS is that my focus is actually on clone production rather than bud production, and I often have old retired mothers kicking around who have outlives their usefulness as clone donors, so I toss them into flower. When they are in veg, I keep them under T12 shop lights with cool white tubes until I need to harvest cuttings off them, then I put them under my MH400 and hit them with N for a week, then feed them bloom fert for another week, then harvest cuttings. The bloom fert is good because a mom at the point of being cut should be very slightly N starved and have plenty of P available so the clones will root well.
Thank you Rock. For an experiment, I thought it came out rather well.