Can anyone give an idea of what is the maximum genetic distance found within some of the older subclades, such as L21, U152, DF27 and DF19?
I don't even know how to tell, any more. FTDNA uses a "hybrid" formula, but it's automatic and they don't really make the formula public. Thing is, it's only automatic for administrators, and only for people in the group(s) they administer. Ysearch GD is way too crude, doesn't include all of the 111 markers, and only works for haplotypes that have been entered there.
So, in that environment -- what's the question, again?