If you'd like some data (for a C172) and graphs to go along with recent posts this is an excellent reference online:
Propeller Aircraft Performance and The Bootstrap Approach: Performance Basics
At one, no several, stages of my life I had Hartzell's prop software coupled with engine dyno (and other) data to aid me in flight performance analysis.
At another stage in my life I trained some Oxford instructors and some would ask why their C172 POH speeds did not match theory. Apart from answering their queries I also stated that they need to teach their students stuff consistent with the exam questions and "correct" answers that they will encounter.