Aussie, apparently, game here in the States are a little easier to kill.
I don't want to be put in the position of defending Winchester cartridges. Actually, I have never used them, my point being that the 55 grain bullets, in the only factory ammunition I could think of, off hand, is by far the best choice. I think I have as much experience with this caliber since the mid seventies, as almost anyone, and if it is used intelligently, I believe it's one of the best 22 centerfires available as a factory chambering. Since I have never fired a single factory cartridge in either of my Swifts, I cannot give testimony. But the risk seems overstated.
Your example seems the rare incident, about like the time I emptied an entire magazine of 45ACP Ball into the frontal area of a coyote and still had to dispatch him with a large rock. I wouldn't cite that event as indicative of the killing ability of my Combat Commander, under normal circumstances.
As I said previously, this gentleman should consider handloading and then we may offer 20 or 30 suitable bullets, as a starting point. That statement I will defend.
Good hunting. LB