Lean temp
RFM says 1650* max but I wouldn't deliberately run it up that high unless you REALLY needed to squeeze out a long flight. Cold winter mornings I'll run 1590, maybe just a psychological block but I can't bear to see it crack into the 1600s. As weather gets warmer, I move to CHT as a limiting factor, use the GEM to view the hottest cylinder and lean till it stabilizes at 400* (should always be #3, usually by 30-80*, sits next to the turbo and furthest from the cooling fan). Again, RFM limits you to 450* (C models) or 500* (F and FX) but that seems blazing hot to me. 1600 EGT or 400 CHT, whichever comes first. Has always worked for me, your mileage may vary.
Flew 7.5 hours today on two tanks of gas. 1978 280C leaned to ~1570, avg fuel flow of 9.8 GPH, avg airspeed of 85 MPH. Love the old C models, very economical and you hardly miss the extra 20HP.