More resolution does mean smoother operation. Overload protection is for when the servo is being stalled out. A good example is when your steering rack is bound-up, either from being too tight or possibly a rock has been jammed in the rack keeping it from smooth operation. This will cause the servo to pull too many amps, thus raising the chances of burning the servo up. Overload protection will notice the higher amp draw thus decreasing the amount of current capable of reaching the servo, this in turn will keep temperatures down and save components.

As for the 5965MG, it would be a great servo for SC trucks.