You could do some testing yourself if you have both lenses of course. What i would expect is that, even when one of the lenses might be slightly better in a general sense, the performance will depend as much on the individual sample. When you buy a pre-used lens, you never know how it was treated, even when it looks prestine. It might haven been dropped or it might have other issues that don't show when looking at it. Only some testing will tell you. The other reason is that even when these lenses were new, they showed small production tolerances. If i remember correctly, it was Ctein who concluded after careful testing that differences between various samples of the same lenses are sometimes bigger then the differences between lenses of various makers..