"It's not unknown for turboprops to bank more than jets due to their slower speed and hence less 'g', but still naughty- but I defy anybody to put a figure to it"
Absolute horsefeathers! For any aeroplane at all, N (or Gz if you prefer) = L/W and is equal to the secant of the angle of bank. The radius of turn is equal to TAS squared divided by the product of the tangent of the angle of bank and g (9.81 m/s/s) - whether in a Cub, Comet or Concorde.
As for estimating AoB - if you have been flying for a few years and are sitting in the back of an ATR with a very good view of the wing/horizon angle, it's reasonably simple to estimate AoB.