Additional clarifications I've added to the OP:

• I define one "payment transaction" as: one wallet paying another in the simple sense.  Additional activity for associated fees, preparing the payment so it can be spent by the receiver, or splitting payment into parts ... should all just counted as part of the one payment transaction.  E.g., buying a cup of coffee = 1 payment transaction (even if miners take a portion, a randomizer service is involved, or behind the scenes lots of activity happens in sub-transactions).
• The baseline configuration I reset nodes to for each test is what I get using this doc starting from the OS I get from Digital Ocean:  https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-vnc-on-ubuntu-14-04  If I need to install other "assumed" items, please provide the instructions.

-cheers.