Excellent points Herb.
I would add that if you fly above mountains or above clouds with ice or above weather you would not want to be in then it helps to know your single engine service ceiling for 'what if', especially if you are near max gross.
I have attached the single engine service ceiling for the P337H - if someone could post for the non-turbo'd Skymaster it could give you a basis for comparison.
Also have attached numbers for single engine rate of climb because if eg. you are taking off from Sedona airport at +20 degC, can you climb if an engine fails in a non-turbo?
One thing these tables do not include is density altitude. i.e. if you lose an engine at near max gross on a very hot and very humid day, can you even maintain eg. 6000' in a non-turbo?
These guys had a turbo but did not follow the POH and push up the MP into takeoff power (
http://generalaviationnews.com/2012/...l-it-cost-you/ ) i.e. 37"/2800". She left it at the top of the green arc i.e. 33" and crashed. What is the max MP on the non-turbo version? And it goes down 1" for every 1000 ft in a non-turbo.
Food for thought...
Also attached the both engines rate of climb for comparison.