Here's some Vortex and Qrazy Train I have going at the moment (this was day 21 after flip) in #3 smart pots with 600W lumatek, I forget the bulb type, I think Hortilux. I use 100% super soil, but it's recycled super soil, probably not as hot as a fresh batch. Also I have had some other strains that didn't grow as well in it--Alien Dog, SAGE, Deadhead OG--maybe because it was too hot. I feed water only, a tea infusion in veg, and some top dressing and/or some molasses in the water if needed around week 5.
Here was The Flav around day 53, same setup, also had good results.
So I don't think 3 gals is too limited, at least for #3 smart pots. Note though that I grow purely for taste and buzz, I don't even keep track of yield. So I don't know and don't really care how much bigger you might grow them with more soil or more watts....