Fifth Wheel Hitch Types (air/flexible/...)

Looking to tow a very heavy 5th wheel trailer (with an F-550 or such).

I've seen 5th wheel hitches that mount flat, hitches that articulate, hitches that have air bags, etc..)

I can imagine that a flat hitch on the truck can flex the heck out of the trailer - so it seems like I want one with air or at least some articulation points in it, but it's difficult to find in 25k lbs or more.

How important are these features, particularly considering that I need to drive over some dirt roads (that's the reason the trailer is so heavy - I got a custom trailer with a massive frame so I don't have to worry about things like frame flex).