i've said this in other threads, but gpw is about the most useless pos way to measure a grow imvho.. it doesn't take into account the time used to get to that number, which is what the op is talking about..
say for instance, someone grows three plants from seeds, they veg them for four months, they like trees, then flip them to flower and flower for another 10 weeks, and at the end, they get a pound a plant under a 1k bulb.. those numbers sound impressive, 3 pounds right?
now we have another guy, he's running sog from clones, 2 week veg, 10 week flowering time, 25 plants, and gets an ounce per, so that'd be 1 lb 9 oz, and looking under a 1000 watter as well.. going by gpw, you'd think the guy who got three pounds did better, but that doesn't take into account that he vegged for 4 months to get that.. the guy running sog could have two complete grows in the time it took the first guy to get his 3 pounds, meaning gpw is about useless imvho.. and in the end of the same amount of time, the guy who pulled smaller numbers in the sog setup would yield more then the guy whole ran trees, but vegged them forever..