There is no way to answer the question of which is best, the double rifle or the bolt gun, without taking in to consideration the ability of the shooter.

I have been a competetive shooter with the "high powered" rifle since 1960. My first match rifle was a converted Rock Island Springfield in .30-'o6 caliber. Part of the course of fire consisted of rapid fire, standing to sitting, at 200 yards, ten shots in 60 seconds, starting with the rifle loaded and including reloading after the first five shots (with a "charger" or "stripper clip"). The course of fire also included rapid fire, standing to prone, at 300 yards, ten shots in 70 seconds, with the same reloading required. Both stages were fired at the "A" target, with a 10 inch "5" ring. Perfect scores were not unusual, so in 1968 the target was changed to one incorporating a 7" "10" ring and a 13" 9ring in the aiming black. Perfect scores became rarer, but not unusual.

My African hunting experience includes two when I was using a .505 rifle of my own design, which duplicated factory ballistics for the .500 NE, weighed 8 3/4 pounds and generated about 100 ft./lbs. of free recoil.

On one occasion my PH was charged from behind by a black rhino. I was standing off to one side and had a clear shot. My first shot hit him in the neck, just missing the spine, the next two hit the shoulder, and the last one (I having reloaded in the meantime) went right up the rhino's rump. My PH, when he got his William Evans .470 DR into action, hit him once in the rump (the bullet tumbled and penetrated only about a foot) and the other shot glanced off the left side of the larger horn as the rhino angled off to the left.

On another occasion I was standing on a rocky ledge overlooking a thicket where native herders had reported a large Cape Buffalo bull taking a siesta. A few well aimed rocks woke him up and headed him in my direction. As he hurried past, I fired four times, three of the shots hitting in the shoulder area in a group the size of a playing card, the other somewhat further back.

I should add that in the meantime the rifle had been converted from a two shot magazine to a three, so that on the second occasion, no reload was necessary. The bull went down so fast that his nose plowed up the ground.

I had a .458 DR with me, but chose to use the .505 becuase of my facility with the bolt action and the larger more powerful cartridge. If the .458 had been a .500 NE, I would have probably used it.
Had I not been trained the way I had been in rapid fire with a bolt gun, and had I not been able to work the action without removing the rifle from my shoulder, there is no question that the DR would have been the better choice.