Personally, I'd be thrilled with 4 1/2 feet of penetration coupled with expansion like that on a buff.

Remember too that the recommended impact velocity range for this bullet is a fair bit less than that generated by the Overkill cartridge. Even so, Geoff has apparently toughened some of these bullets up a bit for you US speed-freaks, the 650gr .577 RNSN being a case in point. For buffalo in particular, I prefer massive expansion provided there is no weight-loss. That's why I choose a soft.