I have a Stihl MS460 that I usually run a 24" bar on. I have used a 32" bar for large trees. I have a 36" for it but haven't used it. I think 36" would cut slow. The 460 is a pretty healthy 77cc saw so you're probably looking in the 80cc class, like a 500i. Or a 90cc class saw like a 660. The...