It will be huge, it will be marketed as the 2 biggest stars in recent times and the biggest fight of all time, the casuals will be unaware of either fighters being past prime
It will most certainly not get near the amount of buys of a PPV fight like the Hatton one, this doesn't feature a domestic fighter and is on at an obscure time in the early hours. If sky make it a PPV it won't do great numbers.
Will do numbers similar to Hatton v Mayweather. Doesn't matter if there is no British fighter, this fight trancends the sport and it will be hyped by the media as the biggest sporting event of the year and the one no one wants to miss. Anyone with a passing interest in sport in general will be watching this.