Everything is relative when you are talking about an internal combustion engine. Bore is the piston size, stroke is the amount of travel the piston goes up and down in the bore. As posted, together this sets the displacement. In general, a longer stroke can equate to more torque, shorter stroke will allow for higher rpm's. The higher the rpm's the more horsepower and this will continue to climb with rpm's. But, there is another thing that they do to change horsepower ratings…a bigger carb or throttle body if fuel injected. A lot of engines, especially marine outboards and such have identical displacements and interchangeable engine parts but have that bigger carb. Yamaha 50,60, and 70 hp outboards were at one time all the same engine save the carb. One other important fact regarding IC engines…two stroke engines fire and make power every time the piston comes to the top…four stroke engines make power every other time. Two strokes have way less parts as well and are lighter in weight. So, for a given displacement, two strokes are always more powerful and rev higher than four strokes. There is no free lunch though, four strokes are quieter, consume less fuel and last longer. As engines go, neither two nor four stroke reciprocating {piston going up and down} engines are very efficient.
As to chain saws…I cut down and mill as many logs per year as just about anyone and have owned them all…you will not regret a Stihl. Reminds me of the joke about the priest and the kid that sold him a mower. Father is trying to get it started and calls the kid over. The kid says, "you got to put a good cussing on it" and father says, "I'm a priest, I haven't cussed in so long I cant even remember how!!" and the kid says, "you just juke on that thing long enough and it'll come back to ya!!!!!" Juke on some Chinese junk long enough and you'll go get that Stihl!!!
