I wondered if a Canon L 100mm would have better AF than my Canon 60mm lens so I hired one (for free thanks Canon) and did some test shots
(I have not analyzed them yet but I don't think there was any difference).
When I sent it back, I realized that it had a filter and and wondered if that had invalidated the test.
I assume that the filter didn't harm the AF - after all Canon wanted to sell it to me.