The actual power output of any engine/prop combo is never identical to the next one & ASI's are also never identical even in the big birds. So end result is as has been mentioned here already if yr tach is saying one thing then that doesn't mean diddly poo in reality:-) CofG also has an effect on low power airframes as someone else eluded to already.
I recall flying an AC50 many years ago that was a dog compared t the others I flew, swore it was bent!:-)
Even the large Airliners have a perf degradation factor entered into the FMG's to help get the best optimum out of the airframe/engine combination, at GA level the same would apply but it's not accurately known.
As for the black LE's? Well hardly any effect would be appreciable I'd say
No two planes, no two pilots are the same.
Wmk2