I'm not a Moots owner but just a prospective buyer. However, I would recommend the Routt 45 so you would have more tire options. Not sure why the just can't design a Routt with short stays and accommodate a 700x45c tire? Other manufactures seem to do so.
It is problematic, in design, for two basic reasons:
A) "Gravel"/CX bikes are based on road standards. Specifically cranksets and bottom brackets--that have narrower tread spacing (Q-Factor) as well as narrower bottom brackets/spindles (based on 68mm standard...as opposed to MTB 73mm std width BB shell). Shortening the rear center makes it much more likely for a 142mm rear-axle bike to have clearance issues AKA the crankarms or rings striking the chainstay
B) Moots works metal. Limiting what can be done to thin out the chainstay
C) Shortening the stays and having 45mm+ tires causes problems for front derailleur clearance. Many CX riders have run into problems with short-rear-center bikes with CX 35mm tires not clearing ETap's FD battery. NVM the FD cage clearing big tires.
Indeed Moots shows a pic of a Routt45 built with ETap, and the battery is just barely forward of the tire as it is.
There are a few ways to solve these problems:
A) Use a "droopy" stay as in the
OpenUP pictured here. But this is only viable on carbon fiber.
B) Use a yolk that adds weight and complicates machining. As seen here on my
Carver in naked frame
https://imgur.com/eecm2Mz
https://imgur.com/rdyLmiP
https://imgur.com/RFBKNAU
https://imgur.com/KIt7M18
And built up with 46/30 rings and 11/32 cassette
https://imgur.com/U9yhfMw
If you read the retail listing the frame, thanks in part to the yolk, isn't light at 4lbs. OTOH it can clear a 45mm tire easily--and honestly probably a 50mm.
The catch with shortened rear-center is that is makes the bike more racey....many riders would rather have a more stable platform on unstable surfaces. My Carver has slider stays that can adjust from 425mm-445mm, and I keep them at 445--even with 42mm tires on. I want the stability for non-compacted surfaces and/or touring with panniers.