I am probably a heavy user here, about 300-350 hours a year in a 12 month
boating season.
I change my oil 4 times a year, using 3 quarts a change and none between. At
that rate I am using a lot less oil than I did with a 2 stroke. It also gets
recycled.
Figure your oil goes in at 50:1 in a 2 stroke, my 60 uses 3 quarts so I could
burn 37.5 gallons of mix but since you usually use a pint per 6 gallon can it
is really 36.125 gallons. That would only last me about 10 hours at a moderate
cruise speed. The oil saving for me is 90% over a 2 stroke. I could even save
more if I used auto oil instead of Merc brand.. If you also add in the actual
fuel efficiency it is greater than that.
I bet the saving is even greater when you get up into the big Vs. His 6 quart
oil change would "mix" about 72 gallons of gas. A 250 2 stroke could easily
burn that on one day's offshore fishing trip.