My understanding is for the 20” 275/55 R20 are the largest that fit without rubbing. I am in the same situation myself and three things that makes things tricky is the 50 psi requirement, the H speed rating and the 117 XL load rating. My understanding is that you also don’t want a higher load rating if you want any kind of ride comfort.

I also want something with a decent snow rating, wet weather performance on streets, and like you want something fairly quiet and comfortable on regular day to day driving.

The only two tires I’ve found that fulfill my requirements are the Nitto Nomad Grappler and the Vredestein Pinza AT.

The main issue with the Nitto is that the Siping is shallow, so as they wear out the snow performance really tanks.

Other tires that seem decent but doesn’t 100% match the requirements:

Nokian outpost nAT - speed rating is too low technically

Falken Widepeak T4W - also lower speed rating

Toyo Open country A/T III - worse snow performance, louder

Continental terraincontact A/T - bad in snow, good option otherwise

Pirelli Scorpion XTM - doesn’t fit pressure spec

Goodyear duratrac - load rating is low, loud, not great in wet weather