I'm currently running WTB Byways 650x47 on my gravel machine. I'm happy with the performance but the clearance between the sidewall and the non-drive side chain stay is exactly one hair's width. No rubbing but it's a potential choke point for mud and other problems if the wheel is even a small amount out of true. I should add that I'm probably running them a bit over the 'new' inflation level on WTB's website; I run around 42 psi but the current suggestion is much closer to 35 for my weight.

My other go-to tires on my commuter are 650x42 Babyshoes. Also nice tires. But is there anything in between 42 and 47? I can't seem to find anything, having looked at Rene Hearse, WTB, Teravail, Panaracer. Is there somewhere else I should be looking, or am I looking for a unicorn?

Somewhere around 47 seems just about right for rough rough gravel/unmaintained roads that I ride; I was thinking 45 would be spot on and not get too close to the chain stay.

I suppose an underlying, philosophical questions is: How much tire do you need on a gravel bike and at what point should you just be on a mountain bike?