" It's not that bad" Really, the recoil of a proper rifle won't knock you over. you won't be varmint hunting with the Rigby or Remington mag, but they can be shot. My Ruger #1 in the Rigby cartridge is a lot of fun. I added a Pachmayer Decelorator pad and about 3/4 of a pound of lead shot and epoxy into the stock. Just drilled a hole and poured the mix in. The gun balances better and the extra weight helps keep the recoil down. I just need better iron sights.
My Remington 700 is a project in the works. Its a Kevlar stocked model with an Answer products muzzle brake. The gun weighs 9 pounds. It needs a protective finish and an iron sight/scope combo. With the brake you can shoot this rifle all day with no pain. I've shoot 30-30's that are more abusive.
The Rigby's great but reduced loads are not its thing. 100 grains of powder are just getting things started. Accurate arms has reintroduced a powder that should allow some load reduction, I just haven't tried any yet. See Marshall's post about the 416 Remington loads and see that 1900 fps is possible. The 416 Taylor is another option, but I ahve no experience with it.
The Remington is the best route for full power loads and a case that will accept lighter loads. Brass is cheap and rifles are abundant.
The direct answer to your question is the 416 Barnes. This is based on the 45-70 case necked down and still gives plenty of power. A converted Marlin with Marshall's LBTs would be a fine 416.
Good luck in your search for 416 perfection,