OUTCAST is mostly correct. The torque that causes the airframe to roll in a hover is derived from the torque the engine exerts on the prop shaft needed to sipn the prop fast enough to hover (thrust = weight). In a constant hover (not bouncing up and down) the torque force is constant.

However, there is another force that works to slow the speed of the roll. This force is from the rotating airflow from the prop as it interacts with the wings and stabs. Same force that requires right rudder on take-offs. This force partially counteracts the torque exterted on the airframe by the engine.

So, that means there is not a simple answer to the question. A larger diameter prop may tend to create a more powerful counter-rotating prop-wash that slows down the roll.

Also, don't forget that a prop is a "wing" that creates lift (thrust) due to pressure differential on the front/top of the blade in addition to force created by raw pitch of the blade. So, lower pitch props create greater lift/thrust (at zero airspeed) while requiring less rotational torque to spin.

This is unfortuantely a complicated subject. The easiest thing to do generally is try different combinations through trial and error until the aerodynamic qualities of different props become second nature.

Jason