Zip is 70592.
Aircooled53, you're right, the freon change is a big factor in this decision to upgrade now.
The downstairs seems to be fine regardless of outside temps, I think
this has alot to do with how much cool air falls down the open stairway from upstairs, and that also contributes to why the upstairs is not as cool as I'd like. The top floor is generally always too warm, enough to draw complaints from visitors. The second floor is ok on the days with moderate temps you described.
I'm gonna visit Carrier's site to check out the model you recommended.
And yes, that was also the type of advice I eventually wanted to get into. I wanted to see what efficiency range was appropriate, then get recommendations for good candidates within that range.
Still have alot to learn, I'm very glad I found this site this early in the process. Thanks.