I've been using the 22/250 and the Swift since 1978 when I moved to Montana. I quickly met and got to know Bill and George from the Powder Horn. These guys are big fans of the big 22's!
At first I thought they were off their rocker, but I also knew how successful they were. Long and the short I started down the road.
I took my first head of big game via a 22 cf with my Swift and a 52 NSB. One shot, down it went! And so it's gone. Deer, elk, sheep., black bear, moose, antelope you name it I've used it or seen it used on them. IME you just can't beat a big 22 for killing out to 500 yards.
The farthest we've taken game is 505 yards, the lope took 3 slow steps and went down and right to Croak City Wyo...
As for the what if the OP had used a bigger gun, Thanksgiving of 92 I shot a big muley at close to 500 yards. At the shot, the bugger just folded up. I mean I dropped the hammer and down he went right now! We picked up and walked over, in the mean time lost sight of where he was at. You guessed it he was gone, and not much blood. Hind site....I would of covered the buck while my buddy hiked over to him, then if the bugger got up I could of hammered him again. Hind sight....oh I almost forgot the round I was using that day was my 700/.340 Wby that I'd been using on chucks to 500 all summer with and the 250 Nozler. Hmm.........
In the last 4 years my wife and I have used our 22/250 and the 60 Horn HP on 26 head of small big game (deer/lope). Of the 26 shots, 24 have gone right down and I mean down and out. Ranges from 35-400 yards. Two have gone a few steps, a muley buck went about 15 yards when and a 90 pound whitey doe taken a bit over 100 yards ran 35-40 yards, I was stunned!
As far as the mono bullet deal, yes they'll definately kill. But, we've found them to do it just a skosh bit slower. Now obviously deads dead but I do have a strong liking for watching them go 4 feet in the air at the drop of the hammer.
Standard cup n core will result in way more DRT (dead right there) shots than the mono's will. Period end of debate. But, like I say both will be dead quick enough.
Bullets we like are 55 Horn w/c, 63 Sierra (I shot my biggest black bear with this load, one shot at 178 yards as he quartered away, bullet entered where his right love handle would be and exited it's Adams apple, said bruin went 30 yards and piled up). We also like the old Nozler solid bases the 52/55/60 and the 60 grain Horn hp.
Honestly, I can't want for anymore when it comes to taking small big game (deer/lopes) and would be more than happy to hunt the rest of my life with our 22/250 (an old 700 with the dreaded factory 14 twist).
Sorry for the long winded post, but I do have a bit of experience with these rounds. I know this from a lifetime of hunting and killing and that if you use a combo, any combo enough that sooner or later something will happen that will make you go hmm..........