My concern with the 100L macro for my intended use is that I've heard it is soft beyond 10-15 feet
This had my curiosity and after shooting new portraits yesterday and looking closer at older shots I must say:
I shot two full body portraits from a distance of about 3 meters. They both show not "softness" but something that looks like slight movement or when you can't hold the camera steady in your hands:
I then crammed in my archives and found other shots taken in distance, here is a portrait that was heavily edited of course but you also can see it was not sharp in the first place
And in a winter shot this also applies
These are 100% crops.
This pulls my opinion on that lens down so much right now I think about selling it for a 135L.
I did some extensive testing of my 100L and discovered that it has mechanical issues in the focus mechanism. It produced similar results to what you are showing, but only did that part of the time. I tested another copy and it did not have the issue. I sent mine to Canon but haven't received it back yet...we'll see and I'll comment when I test it out. But given that, if OP goes for the 100L I'd definitely test it upon arrival or just go for the 135 instead.
Well I calmed down a bit now, the 100L has always been my favourite lens but I highly desired the 135L also. So I decided to finally get the 135L. That will probably eradicate the use of my 100L for portrait work but it's still great for macro and product photography.