The 60 grain Partition and 64 grain PP have been effective on whitetails for me.
Shoot 'em through the lungs with a properly constructed bullet that hits them with enough velocity to expand said bullet and they die,regardless of the diameter of the bullet. If Nosler made a 20 caliber Partition I'd shoot deer with the 204 Ruger.
Guy in Louisiana did just that. Got in big trouble.
Possum cops got his trophy, caused him some serious misery