Your OEM 205/75-14 C tires are rated at 1760 lb capacity x four = 7040 lb of capacity. Plenty of reserve capacity for that size trailer.
The Carlisle HD is a much better tire. I see no benefit of a D at derated pressures when a C has that much reserve capacity. Don't bit into the bigger is better just for the sake of upgrading as at some point a trailer, unlike a truck, can have too much tire capacity.
Now if the oem tires had marginal capacity and the wheels are 65 psi rated then the D at 65 psi makes cents/sense.
"good judgment comes from experience, and a lot of that comes from bad judgment" ............ Will Rogers
'03 2500 QC Dodge/Cummins HO 3.73 6 speed manual Jacobs Westach
'97 Park Avanue 28' 5er 11200 two slides