Transport Canada has been active on this subject, and there is a civil aviation document TP13748E 'An Evaluation of Stall/Spin Accidents in Canada 1999'. It's referred to on the internet in the context of turnbacks, but it's not explicitly available on-line - so it's a suitable challenge for a university library...
I have in my papers somewhere an early 1990s Canadian article on turning back, which contained some numerical analysis and proved to my satisfaction that turnbacks were all but impossible. Now I regard even tree-tops ahead as a better bet.
I shall not rest now until I have found it, and when I have I'll send it to you.
Graham P.