I shot buffalo with a 400 Swift one time back in the day, not because it was the bullet of choice, but it was the bullet/load I had at the time. I had shot two lions already and it was a lion hammer, DRT on both. Buffalo was not on the menu, but a situation came up, I took on purpose behind the shoulder shot, lungs, and it of course worked fine, finding the bullet on the hide, far side.
However, if choosing Swifts for buffalo, with 458 Win, or 458 Lott, choose the 450s, then you won't be as limited in your shot placement for that first shot. I have used 450s in 458 Win, and 500s and 450s in 458 Lott, I would go for the 450s in the Lott size case, extra velocity, still more than enough penetration for a conventional premium soft.
Today I would use only the 420 CEB Raptor for such endeavors, and did, but now retired from hunting......... 420 Raptors are not Conventional Premiums, and behave entirely different. You can also forget SD when talking Non Conventional bullets.