To know what is needed a written load calculation must be done, or you
can under or oversize. Up north here humidity is the main issue and to
large a unit leaves you uncomfortable even at 70f, humidity is our main
concern. A smaller unit is cheaper and you say humidity is not an issue.
Get a written load calculation, with a larger unit since you say its
never to humid you get a quicker cool down comming home to a hot home.
Up north the answer is simple, you don`t want to oversize for humidity
issues.