Outdoor temps for SEER ratings
Its important to understand the outdoor temperatures at which SEER is calculated (BeenThere: you've read this before so please don't beat me up too much :) )
For a variable speed motor in the air handler, SEER is calculated from EERs at representative (seasonal) temperature "bins" starting at 67F thru 102F in 5 degree increments.
The following are the outdoor bin temperatures and their weight% in the SEER calculation:
Now I don't know about the rest of you fine folks, but in Baltimore, I don't run my central a/c when its 67F or 72F outdoors, so 44% of the value of the SEER calc is meaningless to me.
The reason why systems attain 16+ SEER ratings is because they are dual-speed or dual-stage, and they are capable of running on low stage where they have very high EERs at the lower outdoor temperatures where the SEER calc has its highest weighting. Once these systems run on 2nd stage at real-world summer temps, the EER becomes more relevant to operating costs.
I agree that dual-stage systems can enable a higher temperature setpoint since they remove humidity better than a single stage by running on 1st stage longer.
I always like to say "Whichever SEER system someone chooses, get a 12 EER minimum".