Railroad

Not a fan of Goodman products but keep in mind the higher SEER models would require a matching inside air handler/furnace with a var speed blower.

IMO

Well, I guess that takes care of the higher Seer Unit, I have a Sears 125,000 BTU furnace that only has a two speed fan, one for heating and one speed for cooling. I am retired, I don't see how I could afford to replace both, this was the reason for looking at the Goodman, I don't think I can afford the name brand units, and most contractors in my area want to install it. My Sears 3-1/2 ton central Air unit cost $1700, and in the 25 years I have had it, not one problem with it, and about the same with the furnace that cost around $800, which I also installed myself. I would consider another Sears unit, but I don't think the sell units without installation as they did before.

Railroader

If you plan on keeping your existing furnace, then stIck to a good 13 SEER condenser with full coil protection and matching evap coil.

However, I see no reason to replace if existing is relatively trouble free and still providing your home good comfort. No reason though not to do some preliminary research on new AC to get ready for when replacement is called for.

IMO