This is really cool testing.
Check out this thread, the 75_200 no limit firmware should also work for that unit (same layout just 2 mosfets instead of three) and might perform a bit better
A propeller would probably be the easiest way to get a 16kw load without messing with two motors and resistive loads. Cool calculator here. I have the non-demo version so if you give me the parameters I could run it for you.