A bit of thread drift here, but as regards ferrying: The so-called 'wet footprint' in a single is the entire time it is beyond gliding distance to land. The wet footprint of a piston twin will be AS A MINIMUM the entire time it is overweight. Which, from the west coast of the USA to Hawaii would be about half or more of the entire leg. With twice as many engines to fail but being only exposed to the possibility of a ditching for half the distance (until the excess weight is burned off), my attitude towards it was that the odds of going for a swim were about the same ferrying an overwight twin as a single.
Even the turboprops when overweight will have a wet footprint, but not nearly as long for the engine failure case. The depressurization case is usually more of a worry.