Gravel / Gravé / Gnarmac / Groad / ATB

For me its going to be something that goes well enough on road that I can chalk up 50 mile or so on road to get to some awesome gravel roads/single track further afield and get home again without massive drag.

33mm CX tyres still roll better than 45mm tyres because 33<45. Unless you stop and pump up/deflate tyres when you transition from road to mud.

Now, the wellbeing of your hands and back on 100k+ rides is a whole different matter.