I see Avengers 3 and 4 go the opposite way of other Part 1/Part 2 entries. I think Infinity War will gross more OS than whatever’s the fourth one called.
Between 850M-900M is my guess.
I know exchange rate is not favorable right now, but the movie has a really (like really really) clear path free of competitions for weeks (even Han Solo not gonna be that big a competition in the OS markets, and IW should already made majority of its money by then anyway)