[Stephen Benskin]

Further, even if 0.1 above Fb+f is "correct", depending on how you test for the exposure that produces that density, you can get all sorts of exposure index values.

Exactly my point. Stuff everyone needs to be aware of when considering testing.

I'm not sure I'm following the dichotomy of film speed and exposure. Why wouldn't they be different?

Many systems, including Zone System, considers the fix density speed point of 0.10 the same as the minimum exposure / shadow exposure point of exposure. In fact, the just black printing method is predicated on this concept. Film speed is a standardization for comparison between films and a guide for exposure. According to the standard model and not factoring in personal exposure preference, shadow exposure isn't intended to fall on the speed point.