Three reasons why the L version is the way to go, Legendary Bokeh, Legendary low light performance, Excellent build. The 50L is the 85L mini. The bokeh is stellar and the colors pop! I had the 501.4 and didn't enjoy working with it. While shallow dof can be a pain and oof shots are more often I have learned ot just shoot more and when you hit it, you hit it. Since the 50 is the lens most people will find themselves using most in their kit why not go pro quality. I am sure the siggy's are good, i've heard lots of good reports. If i were tempted the Siggy 85 1.4 would be a route i would take. In that case you give up build quality to the 85L. No Siggy build will handle the punishment an L lens will. I've never felt quality craftsmanship in my hands cept the nikon and Canon Pro lenses. This isnt bias talking either.