My GPZ1100 was the same, it kept blowing head gaskets, until a neighbour that tuned them told me the barrel and studs aren't strong enough for the increased power from the 1000cc so he made a set of high tensile steel studs and rebuilt the engine and I had no problems since then.
So it will be very depended upon the quality of the design, materials, engineering and build that will define the durability. Modern motorcycle engines are very highly stressed, when the performance is well used, but well looked after they should be good for 100,000 miles plus.
I agree that you can't beat cc's years ago I knew somebody that had a small engined vw polo where he used to have a 300 weekend commute. 40mpg normally, unless there was a strong motorway headwind, then it would be in the high 20's, worse than a bigger engined car.