They must take new engines on tracks where overtaking is possible or they are stupid as f*** as they can't afford any DNF more. Even with start from behind they will be easy 3-4, speed difference to other is too big. So Austria, Monza are good tracks to take new PUs because Red Bull will be unbeatable there without problems. In Canada they need also new PU because they can't match RB speed there. And overtaking is not that hard on two drs zones. With new PU they are favorites for GB, France, Hungary.
Currently for remaining tracks looks to me like that:
RB tracks: Canada, Austria, (SPA?), Italy, (USA?), Mexico
Ferrari tracks: GB, France, Hungary, (SPA?), Netherlands, Singapore, Japan, (USA?), Brazil, Abu Dhabi
So something between 4-6 vs 8-10, nothing is lost yet. They just need to stop risking with new specifications until they test them in Alfa and Haas.