Very well written Adam.  I must admit there is a lot to be said for a good zoom.  The 100 - 400mm I had was great with very acceptable quality up until end of April this year. That was when I dropped it!    From then on it still worked but was not the lens it was.  The cost of repair was almost as much as a new one.  So that's why I took the plunge and traded it on for a new prime.

 ecurb - The Devil