[link=http://www.rbbi.com/folders/prop/propcalc.htm]speed calc[/link] here is rough speed calc.

the only way to really gauge speed is buy either a 2 points and a stopwatch, fly from one point to another point 100 feet away and time it or a radar gun
unless of course you know multi variable calculus and even then its an approximation. There are just to many variables to calculate trueairspeed,
weight of plane, drag coefficient on the plane and the prop, combo of prop diameter, side area of rudder, length of plane and rpm all effect right turning tendency, even on model this has an effect. Temp density alt and humidity also play a roll.
8200 rpm is perfect, just don't go over 9K. your 8200 will probably go up a few rpm as the motor wears in more