Thanks for the information.
I've seen in other posts that the SEER rating drops when the air handler/evaporator coil is in the attic. Is that because of the heat in the attic sapping some of the chill out of the system before it even gets into the house, or is it because the system is a HV tube system?
I am in an older 2 story home (vintage 1968) and the original AC compressor finally died (I'm sure it can be repaired, but on another thread it's estimated to be below a 5 SEER), so I think that it's time for a new one.
I have seen specs for systems that have SEER ratings near 20 (TRANE XL19i), and many more in the 14 to 16 range. At what point does one typically hit the law of diminishing returns? I tend to be a techno-nut and want to make sure that I don't let myself get talked into something that is the Ferrari of AC. We plan on being in this house for at least another 15 years - so I don't mind spending the "Right" amount, I just don't want to get real stupid with cost.