I'm just an old chunk of coal, no, I mean a home owner-firewood cutter. Dead fall and blow downs with the occasional "big one" on the fence row kinda guy. Trees average 18 to 30+ inches.
20" B&C is most common on power heads in the 50-60cc range, and they seem to work.
My 2171 is one of the "bigger" saws in the circles I run in with a 20"-24' b&c and i throw the 28" B&C when needed.
I like the hi speed/fast cutting the 20" provides when bucking because lets face it,,who wants to stand around all day waiting on an under powered tool to get the job done. I enjoy cutting fire wood but it's still a chore. A job to be done and gotten over with so a guy can get home and enjoy the fruits of his labor,,and pop the cap on a cold and frosty.
Hell, I couldn't even handle, wouldn't want to handle some of these monster saws you guys use. I borrowed an 066 with 36" B&C a few years ago to drop a ?4ft dia.?,, the tree hit the ground, no where close to where I was aiming and the weight/size of that out fit put me in muscle failure!!LOL(it was a wide open pasture and I let every one know this is well out side of any thing I ought to be doing) I'll Never try that again!!!
I'll drink a toast to you guys out there knocking down the BIG timber, on steep terrain with monster big saws.