No, it's not an experimental observation, and I would be a bit surprised if one would actually observe that...
The question was rather prompted by what is in the POH of the C172 I fly; it says airspeed is 3 kts lower when leaned to best economy, than when leaned to "recommended lean" (which is close to best power). But it doesn't say whether or not that is with the same RPM for both cases, thus my confusion...
