I pulled the 7m figure from the Massive Dev Chart as a starting point. I suppose that since I was using Ilford film & developer, I would have had better luck starting with their data sheet. Lesson learned? Maybe.
I've worked with Delta 100 in Rodinal before and was pretty happy with it. Though honestly unless I'm doing a portrait or fashion shoot with my monolights, chances are I'll be shooting in anything from overcast to dark indoor conditions (bars & night clubs). So I had been using Tri-X for everything from EI 200-3200.