Sounds to me like your intended changes are going to move the peak of the torque curve up in the rpm range, but not increase maximum torque. Gear loading doesn't change.
Where horsepower would come into play is if you were running a top speed event and the increased engine power would be used making the car go faster. In this case, the energy being transferred by the rear gears would increase, increasing the heat load into the rear end. This is the reason that some circle track cars use coolers on the differentials.
R.
PS: There are (were) two GM 14-bolt rear ends, the light duty 9.5" ring gear and the heavy duty 10.5" ring gear.
