But if you take that 22-250 and puta "varmint" typebullet in the deer's neck it will drop on the spot!
No - I'm not advocating light calibers as being better, I'm just saying it all comes down to the bullet's design, how it performs at the velocity it is going, and putting it where it takes advantage of that performance.
That same 22-250 bullet through a deer's chest very likely will leave a wounded deer to escape & die later. A big .50 conical through a deer's neck may end up in a lost deer, too. But put that conical in the shoulder and you'll be eating venison.
As for the 800fpe minimum, it's a good suggestion, but not a scientific fact. I'd try to stay close to it as a guideline,and asthe load drops below that figure bullet placement becomes even more important.