To make the right choice strictly from a $$$ standpoint, you have to
figure out how much you will be using the AC with your climate and
lifestyle. What the Sears guy was referring to was that for that
location, you won't be using it as much as someone in Miami, so it may
not make economic sense to go to higher efficiency. You need to
determine what the cost of electricity is in your area and how much AC
units of diff efficiency will use. Factor in that over 15-20 years,
electric rates are only going to go up. But, how long do you expect
to live there? Also, many electric companies are now offering
rebates if you buy a higher eff unit, so I would check that out too.
Many of them have good sources of info on how much electric various
home systems will use too.