ding ding ding!!!
Colin wins the debate.
You see it doesn't matter how fast the projectile is going....It doesn't matter (completely) how heavy the projectile is....It is the combination of the velocity, the construction of the projectile, it's penetration on the animal, and the resulting damage to the vital tissues in the animal (or human) that kills.
Case in point....my 21 yr old wheel bow....shoots slow, 29 " arrows (weight?) and I usually get complete pass throughs including blowing through ribs. The deer are defitnitely dead. The projectile killed them. The projectile was going damn slow by todays standards for bows.

I have a .243, and it is one of my favorite deer rifles and has accounted for many deer...but I don't load it to screaming velocities...just around 2850 fps.

I also have a 50 caliber 24" barreled CVA Frontier percussion cap blackpowder rifle shoting a ROUNDBALL (weight?) It has taken a few deer. They were definitely dead when I started field dressing them moments after being shot with a HEAVY, SLOW-MOVING projectile....soft projectile.

It's the correct combination of Velocity + Projectile construction + Projectile weight + placement

It is not anything vs anything ...Its several things in conjuction with each other.
Now go do your homework and clean your room.