BAD IDEA!!!!!!!!!!
Sooner or later, you're going to have a dismal failure so I consider the screaming fast varmint(ish) bullets unethical.
I've killed several deer with "varmint" bullets and/or calibers BUT the conditions were very controlled and shots were more like execution than hunting.
In "Unintended Consequences", by John Ross, there was a long range sniper duel, I recall the good guys were described as using custom built high velocity 6mms' with "J-4" bullets and at one of the shots, "the bullet blew up". So naturally, I had to look up that kind of phenomenon and indeed, there were actual instances when shooters of high velocity small-caliber rifle rounds would have bullets fragment in flight. Super-fast twist rifling was often another factor that contributed to this phenomenon and the bullets would be described as "spinning apart at the axis of rotation", before fragmenting completely.
There was a thread on here long ago that talked about what was the maximum velocity a bullet can hypothetically travel, and someone mentioned that jacketed rounds can only be propelled at a certain speed before friction with air acts as a solid barrier and destroy the bullet in flight. If that happens right before the impact of the slug with the animal, I can see many ways it can go wrong. If only the core manages to penetrate and inflict a less-than-effective wound channel, that will be unethical.
If you can load the perfect kind of bullet for your intended velocity, ie, a solid homogenous projectile like copper or brass only, anything above 3,000 fps is a guaranteed clean kill. Hydrostatic shock is a real thing and that is why varmint bullet manufacturers advertise "grenade-like performance" and "explosive expansion".
When hunting, I would prefer to have game drop instantly and without further struggle. But the world is not perfect all the time and I have had deer and hogs that ran up to 50 yards before expiring, usually happens when I am using arrows with broadheads. That is still acceptable, but instant drops like the OP described would be ideal. Not only is it unethical to have a wounded animal, but the longer it suffers, the more stress hormones are released into the meat. Eating that meat will cause a lot of problems for your health later on. In China I have slaughtered numerous domesticated animals using "free-range harvesting" where an arrow would be shot through the back of the animal's skull at close range. Think captive bolt gun but with the bolt unrestrained and allowed to penetrate the brainstem and brain completely. Unlike a firearm or steel bolt though, the arrow does not deliver hydrostatic shock or concussion of any kind so there is no possibility of brain matter contaminating the parts that are to be eaten (prions, Mad-Cow disease and Creutzfeldt-Jakob's disease are real dangers). And the result of using this procedure is almost always an instant kill, and when the bow that is used to fire the arrow is at least 40lbs draw weight, clean kills are always the norm. (I have usually used 70lb traditional recurves or takedown survival bows for this particular reason) In a part of the world where there are over 800,000 different kinds of dishes, the quality of food is not toyed around with. Chinese physicians have linked the presence of stress hormones in meat with different kinds of human cancers. That is why I prefer to hunt or free-range harvest and will try not to consume factory farmed meat whenever possible.