Brute, as I mentioned above, it's all relevant and one thing usually affects the other. If you lower your 5th wheel hitch 1 1/2 inches, how many inches will you have between your rig and the sidewallss of your truck bed? I wouldn't go below 5 1/2" or 6" and some here may suggest a greater clearence. A deciding factor to consider....will you ever take that truck off the asphalt or concrete....off road? Going down a level highway that distance doesn't mean as much as it does when you're going in and out of gas station and other driveways....then it can be critical.
Switching to lower profile tires also has a negative side affect...the lower the profile the rougher the ride for both the truck and the trailer and it affects the ride of the trailer more so than the truck.
My first consideration would be to flip the axels. That would raise the ground clearance of the trailer, make it much easier to find your happy level and may well be the cheapest way to go. There other little benafits such as draining your holding tanks, you'll not have to worry about a sewer drain being higher than your trailer, even if it's slightly on the uphill side. LOL
There is a down side to consider. Higher trailer height means a higher center of gravity and so you want to keep that in mind going around a curve...adhere strictly to the speed limit in any twisties.
Let's see what others suggest here?