There is no true max.
Yes, my unit is over sized by many peoples standards.
But with some tweaking. It works the way I like it, and keeps my humidity under 50%.
The amount of time I have setting it up. Most people wouldn't want to pay for.
Not to rub it in too much.
But if it was 100 out, I could get my place down to 70. I'd have to bring my blower speed back up, past 400 CFM per ton though.
I barely do 320 per ton now.
I tweak on mine too, depending on what the outside temp is. Right now I'm running at about 1100 CFM for a 3 ton. It's 100 everyday here. When its in the low 90's and 80's. I'll get it down to about 900 cfm for my 3 ton. It works great, lowers the bill substantially and controls humidity great. It's a Trane 80 furnace, variable speed with 3 ton coil matched to a 10 year old Janitrol. Runs like a champ. I know its mismatched, but I do it for a living and it works great.
There are two customers who keep their t-stat set to 68 in the summer cause they like it cold whn we did the install we went to a five ton from a four ton added more return and supplies i cant believe it when ive gone there program set to 68 and customer has no concern friggin thing must never shut off!