I had one about 5 years ago that I shot ALOT of deer on peanut permits with. It was an absolute laser beam and was bad bad medicine for deer! I sold it to a guy that hunted with me for much more than I had in it and regret selling it.
My dad knew a guy who had one, and we went shooting with him.
Lacking a long range to use it, neither Dad nor I ever wanted one for ourselves. A .223 was plenty to bag varmints or ring steel targets out to about 500 yards.
But, I agree that for those 400- 600 yard shots, the extra velocity that the 220 Swift gives you can be very helpful, especially in wind or if your estimate of range is off a bit.
It has several inches less bullet drop at 400 yards, compared to the .223.
Interestingly, the huge velocity advantage it has at the muzzle (550 f.p.s. over the .223's speed) gets smaller and smaller over the longer distances.
At 350 yards, the .223 will push Remington 55 grain pointed soft-point bullets within 200 f.p.s. of the Swift, if both rounds use the same bullet shape and weight.
At 500 yards, there's only 100 f.p.s. velocity difference.
I read an article yrs ago that the author said that an older hunter said that this cal was one of the deadliest deer rounds at that time. These were his words, not mine fwiw. I tend to like my 200 gr .30 tho, lol.