Need help finding the right 5th wheel weight

Tow rating almost never is the controlling limitation.

Assuming the yellow payload sticker says 3200lb and pax/gear is 600lb...that gives you 2600lb remaining. Call it 2500lb when you account for the hitch itself.

Typically hitch weight is around 20-25% of the loaded trailer (no one goes on trips with an empty trailer, so the listed hitch weight is irrelevant). Using 25% to be safe, that puts you at around 10,000lb fully loaded ready to roll. 

So assuming you want to stay within the ratings (some people will brag about going over the ratings), you are looking at trailers in the 10,000lb GVWR range. You may sneak a little higher but then you will have to be careful of loading and weight distribution. 

I never worried about the "tow capacity" and just went by hitch weight.  take the advertised hitch weight and add about 500lbs to account for the 5th wheel hitch and any batteries you might put in the front compartment and such.. my 5th wheel is 12K and was advertised with a hitch weight of 2300lbs.  that ended up being 2850 when I added the 5th hitch and four GC2 batteries and full freshwater and everything I tank to go camping.  

You are discovering what everyone does while researching RV's (trailers, 5th wheels, and truck campers), they are ALL much heavier than advertised, that dry weight decal is a farce, they all weigh much more.  And your gear will also weigh much more than you think.  There's more than just your clothes and some food, its all the required gear too like hitches, suspension upgrades, propane, additional batteries, fresh water weight, beverages, etc, they all add at least 1,000 lbs.  You need to upsize your truck one or two levels to be comfortable hauling the weight.