Stop in for a cup of coffee

that's not terrible. Depending on the type of unit they quoted you for. My grandfather ran a HVAC business for 40 years before he passed. He always said to go 1 step bigger than recommended for size for your home. Less stress on the unit. and price difference wise is usually minimal if any.
Sorry Chris but that is just wrong. A/C units need to run long enough to remove the humidity. If you oversize your unit it will short cycle and will run long enough to reduce the inside temp to the set temp but not long enough to remove the humidity. You house will be cool but clammy. Before I updated my boiler, I did a "Manual J" study which tells you what you need for heat and cooling. I talked to a HVAC Engineer and he asked me if our a/c runs non stop for a few days when it get's real hot and muggy in July and August. I said "yes it does" He said "perfect". ''That's just what you want it to do."