It depend what you doing, when going out in the woods sawing up dead trees as they lay or fall being a old fart I use my light 50cc saws that I can run all day about 90% of the time. They don't cut that much slower than my 70cc saws which wear me out in a couple of hours. If I was at a landing blocking up big wood then it would be a 70 to 90cc saw. Most of these saws with equal cc's that are well tuned are so close in cutting speed to each other that it doesn't matter. Steve