Just a thought from a non-engineer. While i think the test was good, i don't necessarily think it is conclusive. The test basically measured max flow potential, but the purpose of an upgrade is not to max the system. The purpose is to support x flow requirements. The series test may have been outside the efficiency range, similar to a turbo choking... Its going to overwork itself. A parallel test would be to run all pump options at various flows and then measure current draw. This would be interesting.
As it stands now though i will be purchasing the single pump when needed.