Turns out that I currently have a surplus of both Ilford FP4+ and ID-11 (someone I know had too much of both, etc etc). Just for the fun of it, I'm going to try to see how far I can push FP4 and develop it in ID-11. I'm aware that this combination is not ideal; I'd normally use HP5 or Delta 3200 with DD-X, but this is just an experiment.
Ilford's documentation doesn't cover pushing FP4 past ISO 200 (with ID-11 that is), nor does the Massive Dev Chart. I'm thinking of starting with ISO 800 developed for about 20 minutes with stock ID-11. Is this a good starting point? Or is this just a complete waste of time?