Just to add a data point to the thread, I've noticed that my planes (including exactly the same plane and transmitter but switching from FM to PCM receiver and switching modes on the transmitter) will range check about twice as far with PCM. When I range check I do move the surfaces smoothly up and down so I can tell that the PCM isn't holding intermittently.

Because of this, I fly PCM on anything expensive or that seems likely to have interference problems because of antenna setup. No idea if it's ever solved a problem that I would have had with FM or not.