Just finished converting a Spot Ajax with the Bafang 750 watt motor.
thus far, its close to perfect. It is the quietest electric motor I have seen... The tires are louder.
its fantastic when it comes to running that power thru a set of gears...be that rear derailuer or a geared Hub.
but the motor puts out some serious torque. For IGH folks seem to get best durability from a Rohloff or a NuVinci.
mine is running thru an Alfine 8 for testing purposes... And can easily power up my 28% grade under throttle alone. Its programmable for up to 9 pedal assist levels.... And it does pretty well under assist... Tho it would be slightly better with a torque sensor the Bafang currently lacks.
all in all, I thinks it's the best solution currently available.
word of warning... It needs a normal Bottom Bracket... Won't fit on those oversize brackets on most carbon frames and won't fit on a bike that uses an eccentric BB to tension the chain.