8 inches is a lot. 6 should do it but you need to get the truck riding level to slightly nose down like it is without the pin weight.
I use the Goodyear bags with the wireless on-board air and with a 2K pin weight, I can put in 25-30lbs and get it back to were the truck sat prior to attaching the fiver. She rides good like that. Straight and solid. I do use a Reese Goosebox and that has suspension so I never had a rough, noisy ride. With the Goosebox, I do need to run a little more bed rail clearance over a standard 5th wheel hitch due to the increased articulation the goose gives me. i keep 7 inches over the usual 5-6.
2014 V-Cross Platinum 365VTSB (Bought Labor Day 2014)
TV: 2016 GMC 3500 Denali - Stock for now.
Days Camped 2015: 17
Days Camped 2016: 28 so far