Katy's tour will do Diamonds numbers at best 
She may have high per-date gross in the North America/Oceania but her per-date gross outside the US is not even half of that
If in the UK and Ireland she did less than 1m/900k per date ... Imagine her numbers in the non-ENG Europe 
At least GaGa's per-date gross will go up after the American leg and it'll skyrocket with the Asian leg