RE: My Berkeley Stinson Reliant
I don't have a tach that works, but I'll bet I'm turning around 7000 rpm. An AXI 2212/26 might turn a 9x5 direct drive prop at around 10000 rpm on a 2000mah 3S lipo. I have an AXI 2212/20 intended for speed that turns smaller props at very high rpms but pulls a lot of amps doing it.
There's a guy on E-Zone, Power Systems forum ( Kiwi) that does a lot of testing and can probably advise you best.