250: Thank you for bringing that up, I got side-tracked in my writings. There's a wonderful chart out there that show's what temp/dewpoint combo's have the highest incident rate of carb-icing. I'm lazy and getting ready to depart, so I'm not finding it for you

USMC-sgt: Got it right on the head. When I flew the C310's, I'd fly them at 2100RPM, 25", and would get an equivelant KTAS as running 23/2300, with a slightly lower fuel burn

Mcartier: You're right, they are different units, but obviously related. Just remember that the Manifold is how much coals' you're putting to the fire, the Prop RPM is your transmission, no reason to be using low gear(IE 2500RPM+) when cruising. Lower RPM's also mean that the blade's AoA is more suited for efficiency also. Think of hte foward movement of the prop, vs RPM, and the faster you go, the faster RPM is actually less efficient, than it is as slower speeds such as climb/takeoff. This is regardless of turbo/non-turbo. Although obviously the turbo numbers will be higher. A piper Matrix for example will run 2500RPM/32" max cruise, or 2400/30" for a normal cruise!

FlyandDive: Good points on Mixture, honestly, unless you have a decent/good EGT monitor, it's hard to really tell exactly how close you are. Also, Lycomings have never recommended running LOP operations, just Continental's. I agree that you will be running lower power @ altitude, but we have to remember we are assuming non-turbo in this case. The exact situation would be any time you are running 65% or less in the Continentals if I remember right from the C310(Hence my 2100RPM/25" would be 60-65%, so I'd run it on peak-ish settings, at that point it couldn't produce enough heat to really damage anything anyways.)