For a 1/4 scale Cap elevator, I'd use at least 100oz of torque whether you use one or two servos. Metal gears and ball bearings too.
I almost lost my 1/4 scale cap due to servo failure. I thought 2 Futaba S3004's would be enough. The were until the first snap roll on high rates..... Thank God the surrounding corn was 7 feet tall!!! - Saved my plane.