No one is answering so I will take a stab at it. Seems like an honest question. I've done a couple short test rides on other peoples RTPs. I have a lot of miles on the Snoqualmie Pass tires, which are the same casing as the Naches Pass but in 700C. Back in the day when Huffy and arcane tariffs ensured that nearly all MTBs came with OEM 26 x !.9" which measured out to 40 or 42mm I rode a lot on miles on tires same size as Naches Pass.
The small wheel with the smallish tire does work. Tends to get stuck and bog down a bit in rough terrain. Thirty years ago we were all offroad on the undersized tires and wheels and that is why '29er' took off so big. The big RTP has a lot of diameter as well as width so it avoids the main problem of 559/26"wheels. If you are on smooth pavement and smoothish terrain it will make little or no difference for speed. For plush comfort nothing small will match the RTP.
RTP normally operates at around 30psi. Let some air out to get the wheel past the brakes and then put it back in. At around 15psi the tires should go through. It is not that much to pump back in. Forcing the wheel out is not good practice.
Next question would be what do you weigh? If a lightweight the Naches will have abundant flotation and the loss of super-plush won't be a big deal. If a heavyweight yes you will give up some comfort with a tire that needs 50psi.
Fatter is faster only on rough terrain. On pavement you would need sensitive instruments and it would be a tossup, mostly depending on how perfect that pavement or smooth gravel was.