But then I'm currently thinking if I should get the RF100-400 or RF100-500 for the big body for more reach in some situations.
That EF 70-300mm (112-480 on the M) would cover about the same range at less costs and less space in my bag. And it would leave the big cam free with another lens for a closer range I already own (while I don't own any closer lenses in the M system).
So maybe getting the EF 70-300 and the adapter for the small cam is an option to think about. Thanks for that input.
@OskarB What advantages does the EF-S 55-250 IS STM have over the M variant? I know the M is rather soft, even worse with mechanical shutter and has the occasional IS hiccups, is all this solved with the EF-S? Maybe also something to consider, if it fits the case I use for the small setup.
And like with the Nikon 1 before I consider investing in a dead system.