I'm about 210lb and 5''10 I have a 660 magnum and it's pretty dual purpose but it wasnt always that way. I was always using my ms 260 pro when one day it died or i lost the bar or something.. I slapped a 20 or 22 inch bar on my 660 mag and a brand new blade. First thing I did to that brand new blade was take my flat file and grind 2 or 3 swipes from my cutting height on the blade.
At first that thing was a bear and I was getting fatigued in no time but after 8 or 10 days I got so strong I could wield that 600 mag like it was the 260. It takes some getting used to but it will cut through logs as fast as a hot saw.
It was a bit of a pain switching back and fourth to 46 inch bar for the big stuff but well worth it (Atlanta, GA) city of trees. We have some big trees.
When I fixed my 260 pro and used it it was WAY too slow for me and I mostly do limbing with it then i pull out the butter knife.
It is very important for you to post your results once the problem is solved so that people will be able to reference a solution to their problem down the road. YEARS may go by and someone has the same problem PLEASE POST YOUR "IT WAS FIXED WITH x SOLUTION.