I'm pretty sure INFI <i>isn't</i> tougher. It is harder and more abrasion- resistant, and probably holds a better edge under most circumstances, but in terms of toughness, i.e. resistance to failure from sudden loads, S-7 is among the very best steels in existence, having been engineered specifically for toughness. To the extent that the steel in the Dogfather shares the parent steel's characteristics, it should outclass INFI in that respect.
I think I'll be ordering one (or two). But, for goodness sake, can it be sharp?