Hi Andrew, I've watched this video previously and I think it is definitive.
I have, however, one directly relevant question for you related to the points above about where one starts with working spaces. I suspect the OP may be using photos that are now in "raw" format, but already converted to sRGB either in his camera or application. In this situation is it not the case that having lost all that gamut between raw and sRGB, his options are limited and he will not get any gamut benefit trying to convert a baked sRGB file into a wider colour space?