I appreciate the reply and take note of your comments.
My findings are from a personal real world perspective, I agree the statement of a 300 watt generator may be a little misleading, but I am not a seriously fit person, half fit might be a better explaination.
My choice of using a 24v 500 watt hub motor with lower coil resistance (thicker wired coils) and higher rpm required to start charging a 12v battery was simply from an efficiency perspective.
I suspect the efficiency of a 48v hub motor to be less than what i have found, due to heat losses in the (thinner wired) coil windings.
I'm always open to advice/criticism e.t.c - thats what a forum is for :)
To hopefully learn.