I want to thank all of ya'll for your advice. A load calc was done and showed 4.5 tons required (I watched). I decided to go with the two units (thanks again for the input).
A 4ton downstairs and a 3ton upstairs. Both are dual stage compressors and so quiet that you almost have to be in front of them to know they are on. The one thing I failed to take into account was the size of the outside units. My old system was not nearly as big as the new ones. The tallest one now sits partially in front of a den window so will have to engineer a distraction from that.
All the duct work was rehung (off the attic floor) and rerouted from the original install (20yrs ago), two new return air ducts upstairs, increased the size of the return air downstairs and replaced and enlarged all the return air ducts to both systems.
Additional stuff was a new decking in the attic for the coils/furnace, etc. New drain pan (and a float switch which I never would have thought about) and PVC lines for drain. New gas line to furnace (I like the electric ignition and no pilot light!).
Replaced all of the old plastic grills with new metal ones and caulked all the joints between the vent body and drywall.
Well, enought of the details. Point is in my very limited experience with AC installs, I think they did a very good job and as I've read in many articles, time will tell if I am right.
So, guess I'll give the company a plug and say that based on what I saw and the answers to so many questions while this was going on, AirLock Mechanical in Cypress, Texas did a very good job and worked in a very professional manner both inside and outside my home.
Once again, thanks for all the help.