The torque is the effective moment arm of the motor,
force times radius.
You get more torque on a smaller wheel,
at the expense of top speed,
and you get more torque with more power.
That means that, ignoring differences in weight and
radius of the hub (which may actually be significant),
a 1000W motor will give 4 times the torque of
a 250W motor.
The torque supplied by the 250Watt motor is about
250 * Rh / Rr, where Rh is the radius of the hub
and Rr is the radius of the rim.
I have this idea that the most power could be obtained
by running just the hub with the MW16C -- High Power Motor
(Brushless/Gearless)Voltage:48V Power Rate:2000W-3000W
friction drive against the rear wheel.
It would take a machine shop to design and implement a
friction drive coupling to run it tho.
PS: Tom; I like that you say it is for an electric bicycle in the specs.