But since I only got the 100L, I'd be obliged if you could tell me how much difference there is in the actual shots between 100/2.8 and the non-macro primes. Does "opportunistic" mean that the 100L would by no means serve say as a wedding/portrait lens, or is it just the added minimal dof that makes the 135mm and 85mm lenses attractive?
The DoF is substantially thinner, and the bokeh of the 85L and 135L is better. If there's decent physical separation between subject and background, f/2.8 is ok - my 70-200mm f/2.8L IS II does a good job for portraits. But if you want to isolate a subject from a close, busy background, f/2 or wider makes a big difference.