To complete this thread I'm posting my purchase decision based on research conducted here and my installer's recommendations.
Pursuant to advice from this forum, I obtained three bids from installers with decent references. Only one installer provided Manual J, D, and I believe S information. This installer spent at least two hours at my house obtaining information to complete his calculations and didn't require payment for his effort. To make a long story short, his bid was higher than the other two bids but I chose his bid anyway.
The equipment is Am Std. The winning bid included additional supply ducts (two added ducts upstairs and one added duct downstairs), new return ducts sized properly (20 in), new refrig line sets for upstairs and downstairs, a 100,000 BTU 95% AFUE gas furnace w/ two-stage burner assembly and a variable speed indoor blower, and a 4-ton, two-stage, 16 seer r-410a AC w/ matching evap coil.
FWIW the losing bids did not include additional ducts or new refrig line sets or increased sized return ducts, and the tonnage was 3.5 for both units w/out staging compressors but did include variable speed fans. I understand we don't post pricing here but I believe it's ok to say the difference between the winning bid and losing one was material. So, maybe counterintuitively, in this case the higher bid was, at least in my opinion, more responsible.
The split-systems are identical. One for upstairs and one for downstairs (upstairs unit is a downflow furnace). The installer suggested a 80% AFUE for upstairs but I opted for the 95% and I fully understand I'm not likely to recover the initial cost expense from utility savings but my thoughts are energy isn't getting any cheaper.
I wish to express my sincere thanks for those that maintain this forum and to those that responded to my original post.