Even 14 x 52 sprockets seems like pretty tall gearing considering the typical TW Duro sprocket mods encountered out west tend to feature a 12, 13 or 14 tooth front sprocket and 55, 60 or greater teeth on the rear sprocket. As you note 14x52 w/ a fully inflated Duro approximates stock gearing but you have much more rotational inertia with the heavier tire. My 13X55 Duro @ equipped bike @ 12 psi pulls 55 mph w/o issues up to 8,500 feet elevation or so, then comfortable top speed falls off as elevations increase.
While circumference is a handy metric what your bike sees as a final drive ratio determinate is the loaded tire radius which is a function of tire pressure. This is the measurement to consider. Lowering a 26x6x14 Duro’s pressure to 6 psi or so reduces to loaded rear tire radius to approximately that of a stock tire @ 14 psi. This is a good trick in the nasties. Low pressure not only creates greater ground contact surface area but reduces driven radius and thus lowers overall final drive ratio facilitating greater torque at the rear wheel.