I would try the 9s big ring in the first instance; it might work well enough for you to at least make a good decision about the size based on experience.
True enough
I wonder if an improved softare release might include an optional overshift function?
I haven't looked at it too closely but it looks like there is potential to be able to fine tune your shifting to the nth degree. TBH I'm personally none too keen on these battery powered derailleurs esp from the standpoint of having them on a bike that will be used on tours. I'm already sick and tired of trying to keep all my devices charged up e.g. rear LED lights, mobile phones, cameras, powerbanks ....no! No way