I appreciate the skepticism. But if you are going to call doubt on my statements then I think you should at least back up some of your claims, it's only fair.
I have had lots of experience behind both lenses on my 7D and I can assure you the autofocus on the L version is much faster. Just intuitively, that seems like it would translate to other bodies as well.
I suspect that your old 100mm lens is, as you say yourself, a clunker. Its a well known issue - here is an exerpt from a review of the older version http://www.the-digital-picture.com/Reviews...ens-Review.aspx
"Utilizing USM (Ultrasonic Motor), the Canon 100 Macro internally focuses very fast, quietly and very accurately. I've been questioned on the fast AF statement several times since writing this review. I've rechecked my lens and, though it takes a little time to go from 1:1 macro to infinity, it focuses very fast at normal focusing distances. The second person to question this exchanged their lens for another - the replacement was much faster than the original lens they received. This would indicate to me that there may be an issue with some samples of the Canon EF 100mm f/2.8 USM Macro Lens".
So maybe you should try another version of your non-IS lens for comparrison.
As I was very interested in upgrading to the IS at one point , we did real life tests with both lenses in typical underwater low light low contrast situations. We tried them on 40D, 50D, 5D and 5D2 and we could honestly not tell any difference in autofocus performance. But then autofocus is a function of lens, camera body and custom functions so I concede that there could be a difference with the 7D but I doubt it. On my recent trip to Ambon there were two 7D shooters, one shooting the old 100 macro and the the other the new IS one. They were both happy as Larry!
Not skepticism, just realism 