With the right strain, if you wanted 1 lb plants, you could do 2 plants total in 15ish gallon pots. Say you have a high yield 8 week indica, if you veg it about 8 weeks, staying on top of lower trimming and topping/training properly you could conceivably do 2 plants at a lb each. In my experience a lb is more like the upper end however I know it is doable.
For the other guy, in a 6000w, 6 plant grow, 1 lb per plant is a no brainer imo if done correctly. Especially with CO2 and proper environmental controls. If I was in a situation to dedicate 1000w per plant, I would definitely try to push higher. I've heard of people doing like 5 lb plants indoors, I've just never tried to push past the 1 lb/plant barrier myself.
This would however require a long veg period, I duno if a beginner grower would really have the patience for it. Unless you are in it for the gardening and not the product.