20’s arent required on the max tow. I went with the 18’s for hopefully a better ride and honestly I like the look of the sport wheel 18’s better than the 20’s for the 2021 models. (just me, and I wavered based on looks) I have 20’s on my current 2016. They look nice but not worth the money to me.I don't believe the max tow will help with payload as it may actually hurt you. Depending on the configuration the max tow may force you to 20" wheels (+30lbs - another rant is that I absolutely hate lower profile tires on a truck but that's a discussion for another day), larger rear brakes (+?), different bumper (+??), etc.
I think The only way to get the really high payload is the HD payload package but that’s not available on the sport models and I don’t need that much payload to sacrifice some other things I want for the other 50 weeks a year I’m not pulling a trailer.