I know I mentioned it. Maybe I was too wordy. True, with equal servo arm and control horn lengths the mechanical advantage is one and there is neither an increase nor a decrease in torque. But the reason why you don't want to use a 2" arm instead of a 1" arm in your example is because given the same amount of desired control surface deflection, the 2" arm will move about a smaller arc, thus using less of the servo's resolution and you'll be operating closer to its deadband region. Likewise, any slop in you linkage will be more noticable if your servo's full operating range is within a 20 deg arc as opposed to a 40 deg arc. And lastly, a 2" arm will experience much more bending loads than a 1" arm, possibly causing unwanted deflections and even failure so it would have to be appropriately beefed up. The only advantage to the 2" I can see is better linearity response because there is less rise and fall of the pushrod due to less arcing (but that can be taken care of with expo).

-Tim