What are the pro's and con's of a shorter stroke (3/4" vs 1.25") and how
does the orbital action feature work (and why whould I want it) ???

I'm looking at a Milwaukee 6509-xx (where xx is a number like 20, 21,
22). Anyone know the exact differences between these model numbers?

I'm looking at the Milwaukee because it seems to have the least amount
of play or wobble in the blade and the shaft mechanism vs other saws.