I can only share my experience.

My Mom needed a new furnace last year for the downstairs and upstairs - 2 apartments. Bottom significantly bigger than the upstairs. Furnaces were from around 1967. Heating guy says the furnaces were oversized so we split the difference between the calculations and what was installed. The results were very good. Asking around found out that in the past the calculations were not very accurate so everyone oversized furnaces.

Oversized furnaces are not good. My Mother in Law's gas furnace is oversized and short cycles. It is not pleasant heating because of it.

On the AC side, 5 ton seems too big and 2 1/2 ton seems too small. I'm in Cincinnati 2 story 1900 square feet and have a tight house and have a 2 1/2 ton heat pump. Seems about right.

I would lean towards the smaller units.......... Maybe 3 ton on the AC.