Right in that case I think we should upgrade OGM too, also people will be happy that we will use the same WriteConcern as the driver by default: less confusing.
You choose if you have time to fix OGM first, for me it mostly important that we can keep using the same versions across this module and OGM, or we won't be able to use them together as we'd like to. Of course we won't always be able to keep them perfectly in sync but since you say they changed the API this looks like an urgent concern. Could you start by opening an OGM issue?

 /cc @emmanuelbernard