Avoiding dumpster fires and minimal competency should get you to 40-50g/sq ft. Clones of behemoths or extremely good luck with seeds (genetic variety) will get you to 70g/sq ft. Supplemental CO2 should increase those numbers, but i don't believe it is cost-effective. IF you have the choice/possible, increasing growing space is financially smarter than adding co2.
you can use these rough estimates to compare your results and make more informed decisions about improving your methods.
35-40 dli, give or take, a fairly well-controlled climate and not overcrowding your canopy is all you have to do for excellent results. Having a goal for your canopy helps a lot. Shoot for 3 colas per sq ft and make it happen in the most efficient way possible. I'm always trying to find ways to cut my vege time while maintianing yield per plant.
Yield is only half of the equation for productivity. Time also matters. It doesn't matter if you get to 70g/sq ft compared to 50g/sq ft if it also takes 140% or more time to get there, for example. That's a wash over the long-term.
if you grow from seed you'll less often max this out. Genetic variety can be slightly mitigated by culling the weak, but clones are the only way to expect upper-end yields constently. I germinate 150-200% of need and happy with consitently clearing 50g/sq ft. One hermie needs to be trashed and those numbers go out the window. roll with it.. good to compare but be reasonable about it.