A Leupold 1.5-5x or 1.75-6xE works very well with the Ruger mounting system on the rib. I don't think I would go with a larger scope than that on this rifle. Kahles has a very good 30mm tube scope in the 1-4x.

First thing to do with the No.1's is seal the wood where in contacts the action, seal the barrel channel also. Then shoot it. It may surprise you with it's accuracy. You may need a good trigger job on it. The new No.1 triggers aren't the greatest in the world right out of the box.

If you are going to be shooting this from a bench, make sure to pay attention to where you rest the forearm across the rifle rest. All of my No.1's have prefered to have the action on the rest, instead of the forearm. Forearm pressure can have a small effect on accuracy. You can actually "tune" the rifle a little by tightening/loosening the forearm screw to the rifle's prefered forearm pressure.

If your Rigby has one of Ruger's old red recoil pads on it, you will want to replace that thing. It's hard as a brick.