Just an update for those interested....Copy 4 of this lens arrived on Monday....I have been putting it through a series of tests. Sharp lens. Much sharper than 24-105 f/4, including at 70 mm (unlike copy 3). Maybe slightly sharper than the 70-200 f2.8 II at 70 mm (very similar). No odd issue at 70 mm as was observed with copy 3. AF accuracy is better than previous copies, 97% at 24 mm and 98% at 70 mm.

But, there is a small bubble in the front element. My small, about normal dust sized.

I am off to work still thinking about if I will keep, return to adorama, or send to canon under warranty. Leaning toward keeping this one. I doubt a very small bubble will influence many shots. Anyone have experience with this?