props: tractor v pusher, q tip, ducted?

If one uses the Cessna 377 Skymaster as an example, it's pretty clear
a pusher prop is more efficient than one pulling. The data seems mixed
though on q tip props -- any leads as to where there may be quantative
data? What I found suggested the extra length of the prop might just
as well go to increasing its radius as in decreasing end vortix
effects. Finally, does anyone know of any work on small airplanes
using a ducted prop (shrouding it rather than using the q tip bent
end? I'm not worried about ease of flying (the problem with pusher
props are pretty obvious) but rather with converting the horsepower
delivered to the prop into usable thrust, that is, getting the
greatest efficiency (miles per gallon is a crude way of expressing it)
for a small single.