I shot a LOT of coyotes with the 60g Sierra Hp in zero freebore 243's and 6 Remingtons, and they kill very well, break hips, ribs, shoulders.
75g Sierra hp does very well also.
80g sierra blitz bT is a fabulous coyote bullet, with a very, very loud plop when the bullet hits, good penetration.
All of these sierra's give fantastic killing ability, even when hit behind the diaphragm. 70g Nosler ballistic tips are tougher than all the above.
No doubt in my mind that a 55g Nosler ballistic tip in 6 mm would be a fantastic bullet for coyotes, speed kills.