[simplyaccont]

There is actually good reason to bump up capacity by half a ton to ton, unless currently installed unit was sized recently. The reason for this it's that design temperatures jumped up, sometime in a big way in a recent ashray published design conditions (and many companies don't even know that this is the case and use those from 10 years ago or more). And even the published numbers tend to be off and they usually use one specific weather station in a region that may or may not have same weather as you.

When I replaced hvac a couple of years ago, I retained company to make manual j calcuation as none of hvac contractors were willing to do it. I provided it with design temperatures that I calculated after scrapping data from a bunch of private weather stations in few miles radius