Actually, the easier way is to look at the distance between the flap trailing edge and the bottom of the fuselage (some LAME's count exposed threads on the adjustment turnbuckle) then look at the aileron trailing edges compared with the flaps.
Another common differences are incorrect calibration of the tacho (ie you are doing more or less RPM than you think).
Cruise speed on the Cherokee 6 varies a bit depending on CofG position. Does one aircraft carry more junk? Or radio's down the back?