Originally Posted by Emilio700

Depending on what mud clearance you think you need, 42-43mm actual width is doable. I think the frame itself has enough shock absorption that the 650b volume thing is obviated a bit. That leaves actual traction from the 650b to match. The best full tread 700c gravel tires have lots of grip when run low enough. I've been running 30 front, 34 rear psi in my Pirelli Gravel H's. No bottoming, comfy and very grippy in dirt. The Gravel H is a near slick in the center so a taller tread would be even better grip. To me, 650b is a single track or pure rocky trail tire size. 700x40's should do everything better in most gravel use cases.

That said, wow, 650b on a Domane!