ive done a few where I had to cut out blocks to shorten a stump because the 42" bar wouldnt double cut it, took over a full day to bring the stump down from 4ft to 6"Unless you're cutting a tree over 12' across, the shorter bar will be faster. 6' bars are for West coast redwoods.
I run a 28 on everything, if im at the point of using a 6ft im in 12+ ft stumps or milling
we plan to mill some massive stuff, going to build a sawmill capable of doing 8+ft diameter logs
im never going to grab an 881 with a 6 or 8ft bar just for the hell of it, and sure enough not buying a $600 bar unless I need it!