5th Wheel Hitch Weight

Hey guys, my wife and I just bought our new 2017 Ram 3500 Dually diesel to tow our 2017 Grand Design Solitude 375 RES-R. Now we are trying to choose the right hitch for the combination.. We are looking into a Curt 20k lbs hitch, but want to be sure this will be sufficient enough for what we are towing. I'm not sure how much additional weight is considered a safety margin, but we were originally looking at a 24k Curt.

If we go with the 20k, will we regret it? Thanks.