Also the hardness/density of the timber has a lot to do with bar/chain selection.
Here a mid 60cc saw can only handle up to a 20" bar in hard as nails Box (eucalyptus albens, eucalyptus melliodora) and even then it can bog in larger logs/trees.
A 75-80cc saw is maxed out at 28-30", maybe 32" for a Dolly 7900 in Red Gum but 30" is about the comfortable limit in Box.
Longer bars need a 660/390 or larger.
Here in pennsylvania Hickory trees are very hard. Especially when frozen. They can make a saw work hard in a hurry. They can also make a saw go dull in a hurry. Shorter bars keep your rpms a bit