[marzetti]

I am designing a single axis linear positioning system and am considering using servos as opposed to steppers. My question is will a servo provide sufficient holding torque or will a brake need to be provided? This will be a setting a saw stop so it has to withstand the possibility of the stock bumping against the stop and moving it.

[Al_The_Man]

The very definition of a servo is that the force or pressure etc exerted should not result in the accepted following error to be exceeded, so you need to calculate the force and allow for it in the servo design.
IOW, the servo should always be in control.
If deciding on a brake, the servo action would have to be removed when the brake is on, any disturbance of the servo position is kept track of and ideally the servo adopt the new or changed position when the brake is removed, if this is not done the controller will attempt to correct the error and a servo 'jump' occurs.
Al.