In our tract housing community in Maryland (where today we had a high of around 90 degrees with 50% RH), a neighbor just had a new Evolution 18 heat pump installed today (by a reputable firm in the area), and it's a 3 ton, for probably 2800 sqft. total conditioned space. Another neighbor down the street I already know has a 5 ton single stage (Goodman), and it's zoned for each level . Not sure who's got the better size for the heat gain, but someone's certainly way off with a 2 ton difference in sizing.
Personally I think they're both a bit off for this model home . Nevertheless, the importance of a load calculation is evident here, when you have such drastic sizing discrepancies.
This post has no real purpose but to describe my recent observation, and to add to the importance of getting a load calculation done when the need exists.