Other than the fact that you may enjoy doing all this,knowing the free load RPM of any motor,is just not usefull in any way.
Apart from the fact,that the power sousrce you are using,will undoubtably be different from any track you run on,there are so many factors involved.And very few of them even to do with the motor.
Track power,track wiring,track surface,track configuration,track temperature,humidity,track conditions(clean,dirty,glued,un glued).
As well as the free load RPM,you need to know the torque characteristics of the particular arm/setup combination.You can take ten seemingly identical Superwasp motors,and have ten different no load max rpm readings(and,I mean huge differences,of several 1,000s of rpm).Now the good news,do this on another source of power,and everything will change again.
The one thing I can guarantee you,is that the max RPM reading will have ABSOLUTELY NO CORRELATION WITH ON TRACK PERFORMANCE AT ALL.
As I said,there are too many variables in the motor,and in the track,and chassis.
While you are spending untold hours charting moto performance/RPM,most other people with 10-20 minutes worth of track time will be blowin past you on the straights and out of the corners too.
By all means,enjoy what you are doing,but,I would rather spend the time actually playin with my cars.
For the Super Wasp,just go with the smallest pinion you can put on it.That will usually get you close,and go from there.