don't know if I can add to this discussion, but I would still like to point out that Agfa Rodinal is not a fine grain developer. It's sharpness however, is outstanding, and I guess that's why people like to use it.
As far as exhaustion in 1+100 dilution, I have never experienced it, since I always use 50% more developer solution than really is necessary for my tank.
I have never tried to develop under 68*F, but will give it a go and see if there's an improvement.
Personally I use Rodinal only with ISO 25-100 films. Any film over ISO 100 I try to find alternatives.
I tried FP4+ in Rodinal, but like someone suggested, I too shot it at ISO 80 to get some more shadow detail and slightly reduced grain. It was a fine combination.
Currently I'm using the Efke line of films, and they all work great in Rodinal and even better with Tetenal Neofin Blue.
Anyway, hope this helps,
Saint Paul, MN