I've always used 6.5 ft bed trucks, don't use a sliding hitch and never had a problem (26+ yrs). At times, with older design fifth wheels, I was limited to about 65 degrees max turning angle, again never an issue. Differences in payload are minimal and not part of the reason that I don't use an 8 ft bed. Besides unless you go with a manual sliding hitch, then the added weight of an auto sliding hitch offsets part of the higher payload of the short bed truck anyway.
If I was that concerned about both payload and max turning angle, I would probably opt for the Sidewinder pin box with a short bed truck. It also has advantages over a sliding hitch, faster response when backing up and the back of the pin box can't hit the sides or tailgate of the truck.
