I'd like to credit A and C for being the person who made me actually read the placard in the cockpit of the PA28-180 Archer I I fly (which belongs to him) - which resulted in me flying at a higher RPM than previously. I'd been using 2300 taught to me at a previous flying school - he pointed out that this was below the 65% setting according to the placard (2350 at SL, more of course at altitude).
RTFM, for power settings, I'm afraid, unless they are placarded. Or make yourself a ready-reckoner for the cockpit.
Tim