It is much easier to adjust the Reese hitch height than it is to adjust the pin box height on your 5th wheel. The four 1/2" nuts on your hitch require 75 lb. ft. of torque. It might be a slight struggle adjusting the hitch height alone but it is very doable. The 5/8" nuts on my pin box require 135 lb. ft. of torque but they were a big chore to remove and required a helper. I recommend leaving the pin box alone and adjust the hitch height.
Just be sure to closely check your clearances while turning on uneven ground. As has been mentioned, 5" or 6" of clearance on level ground is a common amount but always watch things closely when maneuvering over uneven ground.
2015 Wildcat 282 RKX
2011 F350 Lariat, 6.7 L. Diesel, 8 ft., SRW, Reese R20