Thanks for your reply and nice bike!
Yeah I was thinking about just running 700C with some 40s, should be more than enough for gravelroads and such. But it would be cool if I would be able to ride some mtb trails as well and than I prefer wider tyres.
I have a Koga Randonneur - look a few posts up.
With 700CC mine easily clears 32s + big mudguards, you could probably run 40s without mudguards. As such I've never needed a 650b.
Only problem is they're quite rare.