Got 338WinMag and 375H&H, but got no single shot high power rifles.
Other than a smoke pole I'm ready to get rid of, I don't own a single shot rifle, shotgun, or pistol of any sort.

Really, I don't consider myselfperfect enough to feel good about utilizing single shot rifles for any sort of big game hunting.
I'd take the Howa in 338 WinMag.

All my centerfire rifles are single shot. The ruger No 1 375h&h is actually tamed in recoil compared to most rifles that I have shot in that caliber. And it also will shoot cloverleaf groups. You can put atleast 30-40rounds down range before you start to have the ouch factor without a brake or fixed recoil absorbing rest. I've shot the howa's my friends have bought and there's some recoil.

I have been using single-shot rifles since 1953 when I got a Winchester Model 47 .22 LR. On any given outing with that little rifle, I generally managed to shoot up about as much ammo as my buddies with repeaters of various persuasions, including semi-autos. I could keep shooting, one at a time, but theyhad to stop shooting to fill up a clip or magazine, so thetotal number of shots we could get off in a given time worked out to be about equal.

However, it is a fallacy to believe onehas to be "perfect" to use a single-shot for big game hunting. Over the years, I have found that it is desireable to kill your game with the first shot, if possible, since often critters don't give you an opportunity toshoot again. I assume you subscribe to this idea also, since you are undoubtedly a concerned sportsman. Yes, it does happen, but the Ruger No. 1 can be reloaded for the second and subsequent shots just about as fast as a bolt-action can, if you carry the extra six rounds in a buttstock cartridge holder and have done a little practicing for fast reloading. Yes, fast repeat shots with a single shot require a familiarity with the operation of the SS action. But it is just a different set of manual actions than those used to operate a bolt rifle.

Whenusing a single shot for dangerous game, one can hold a couple of extra rounds betweenthe fingers of the left hand (assuming one is right handed) while aiming for the first shot, just like the guys do who use doubles. If you practice reloading this way, you will find you can drop the block and slam another round into the chamber and close the block just as quickly as a person can cycle the bolt when using a long cartridge like the .416 Rigby.