My 14" tires on my boat trailer OE were "C" full inflation 50psi and I went to same size in "D" and I run them at 50psi. Weight/inflation chart dictated 45psi based on load. I always add 5psi (per GY Tech) when up sizing load range so 50 is the perfect number as I have towed at least 25k at that pressure with perfect tread wear.
Bonus of having extra capacity if needed was when I recently had a total hub bearing failure and aired up the one tire to 70psi and towed home on back roads for 60 miles with the single tire only getting to less than 120 degrees.
