I really want to read all your hunt reports with that rifle.Agreed, it's the diameter of the bullet, given that the construction and design of the bullets are similar.
I have found that, within reason, diameter and design of the bullet is more significant than the velocity.
As mentioned, I have killed several cape buffalo with 410 grain CEB Safari Raptors in a .50-110 Win. at 1,950 fps, muzzle velocity. All one shot, double lungs. DTR.
Brian