Sounds like a perfect set up for a Turgo and well within reach of a Pelton. I think at that head an impulse turbine will work out far cheaper than a reaction turbine with its large diameter draught tube. The Banki will never reach the performance of a well designed reaction or even that of a Turgo or Pelton, but its simplicity and tolerance of crude construction will likely keep it ahead of your simple propeller turbine.