As a new grower I use gpw as sorta a milestone in my learning. When I first started I was at .25 if that. I tweaked stuff then hit .4, then .5 now I just hit .7 on my harvest 2 weeks ago but until I repeat it I don't count it. I tell myself when I hit 1 gpw I can relax a little & just grow.
For me what matters more is the profit/cost ratio. How much does it cost you in dollars including your time in the room compared to the output. If your in you room for 40hrs a week to produce a couple oz it's not worth it.
This is just an example:
clone/cups 30 days
1-600 watt veg (30days) 600 watts power per hr x 18hr = 10,800 watts per day
2-1000 watt flower, 60 day harvest. (2160 watts power per hr x 12hr=25,920 watts
a/c-1,260 watts per hr x 10hr = 12,600 watts per day.
dehumid-6000 watts per day
10" fan-236 watss/hr x 12hr = 2,784 watts/day
6" fan-116 watts/hr x 24hr = 2,784 watts/day
nisc fans-200 watts per day
Total per day = 61,088 watts +/-
Electricity 120 days = $1,123.20 (example at my house)
Promix,nutes,misc. = $100
cost to grow a 4 month harvest not including start up cost & personal time is $1,223.20
Now you have a baseline for the 2 lights.
think of it as price per oz rather than gpw.
Let's say you produce 32oz (lb per light)
$1,223.20 (cost) / 32 oz = $38.22 per oz to make.
if you produce 2 lbs per light then it's $19.11 per oz to make.
Now I dont care what the price is in your region because what you pay for heat in Canadia some else pays for a/c in Arizona. It's all in the same ball park.
And if you produce 6 oz per then it's costing you $203.86 per oz to grow. still better than street prices i guess lol
My .02