The .500 Nitro is not so brutal as you seem to believe. The typical British double rifle in that caliber weighs about 12 lbs, and is fitted with a recoil pad.
Consider that the bullet only weighs 70 grains more than a .458 Winchester (570 vs. 500 grains), and the muzzle velocities are about the same.
The bolt actions for the .458 typically weigh 9 - 9 1/2 lbs, and are fairly brisk to shoot (they should be a bit heavier - mine is a custom rifle built on a Remington Model 30S action, and weighs ca. 10 1/2 lbs. and is not unpleasant at all).
My .500 Nitro, on the other hand, is a Merkel DR, and only weighs 10lb. 4oz. - it is a bit lighter than I'd like, but with a decent recoil pad it, too, is not unmanageable, though you do know you've done something when you pull the trigger.
If you want brutal, try the .378 or .460 Weatherby in a factory rifle.
And, one of the most unpleasant rifles I've ever shot was a Ruger #3 carbine in .45-70 with fairly brisk (but not maximum) handloads - one shot was all the fun I wanted.
PRD1 - mhb - Mike