.....the DOF at 135/2 is something that the 100L can't touch in any lighting at any time and place.....
John, with respect, that just isn't true.
We had a very acrimonious thread (from which I believe many posts went astray) on those two lenses, I actually posted examples from both wide open and not one person correctly identified the images, even very vocal f2 users. Sure if you take two images at the same time from the same place it is easy to tell, but use both on the same shoot naturally and it isn't, use both to their full advantage in different scenarios and it becomes impossible.
Faster focus for sports: 135.
IS for lower light or shutter speeds: 100.
Maximum light gathering potential: 135.
Close focusing: 100.
But these are not IQ differences, they are functionality differences or user requirements.