Your temperatures are most definitely warmer than mine (can I move into a spare room in order to warm up, lol). The other day, I closed my grow space off as much as possible and ran the light for hours (less than 18, but most of the day). IIRC, I managed to get the temperature in there up to 62°F - and then I turned off the light and opened the space up so that I could get some of that heat into my bedroom. Within an hour, the temperature was back to around 50°F.
But, from late Spring through mid- to late-Autumn, I can get it up to 102°F, easily
.
Are your plants getting rootbound in three-gallon containers? Are they running out of nutrients before the grow is finished (perhaps growing with some kind of method that depends on having nutrients in the soil to begin with instead of one that allows you to feed the plants over time)?
If this isn't your plants' limiting factor, then I don't see where it'd do much good. Going from three- to five-gallon containers would mean the weight will be that much more - which could be significant if you have to move the containers around regularly.
My first guess was temperature, BUT the differential looks fine and your lights-on temperature, while low for the average strain receiving the maximum amount of light that it is capable of processing, is likely also fine for the amount of light that the plants are receiving.
Larger buds do not always equate to a larger yield. I've seen a few "giant fruit/vegetable" grows, and the growers always seemed to remove all the fruit/vegetables/flowers except the ONE that they were planning on entering into a contest. A 20-pound tomato might look awesome, but I'd rather have 50 one-pound ones, lol. It's been a long time since I tried to grow large buds (and they weren't
huge, since every one of them was shorter than from my elbow to fingertips). Then I got onto a "scrog kick." Later, I realized that even a small bud is too large to fit into my bowl after I grind it up
.
It might be that, if you kept the same amount of light but decreased the size of the space, you'd end up getting a higher yield per plant (and denser buds). But even if that's the case, it wouldn't guarantee that you'd end up with a higher gross yield
per watt. It might be that, if you were to make such a thing, that you'd end up feeling that you were spending less effort growing - but the opposite might end up being true, too, IDK.
You could try adding more light (and more intense light), getting a few rabbits, and placing their cages high up in the grow space. They'll add CO₂ (although, depending on your ventilation, it might leave almost as fast as it was produced). And, since all they do is eat, poop, and make more rabbits, you would have a potential source of fertilizer (after it was well composted, I assume) and meat. I've never eaten "caged" rabbit because it's too easy to just go outside and get one, lol, but they'd probably be okay.