I'll second Ted's post. I ride a Pugsley with 3.8" tires ... the tires, tread & pressure are the most important thing on soft conditions (sand or snow). Invest in high thread count tires, making the sidewalls softer at lower pressures, that is more important than 4 vs 5 inch tires.

I run Fat B Nimble in the summer for mostly gravel roads, and I run Dillinger4 in the winter for snow and all the fun winter stuff. I'll run the Dillinger4 tires under 4psi (~210 lbs rider with Pug), and I can ride unbroken trails ... it's will wear me out quickly, but it's ridable.

Frau Toad has Jumbo Jim for her Pug, and if I was picking a tire to focus on sandy conditions, I'd go with the Jumbo Jim.

This article has good info on tires for sand:
https://fatbikeplanet.com/5-best-fat...d-riding-2020/