Probably pretty low. What's the payload sticker on the door say?

 

 

 

The attached file has the specs for 2017's; likely yours will be same. Looks like the payload (page 39) ranges from 5800 to 7600 depending on your actual configuration. Page 59 shows rear spring rates. I can tell you my F-350 SRW squats 3" with my ~3500 lb camper. Your DRW has springs roughly 50% stiffer, so I'll guess that you'll have 3" to 4" squat with your 5k load. But I added upper and lower stable-loads to get my squat down to 3" - before that it was in the 4 to 5" range. It would be awesome if dealers would make this info available before you buy . . .

 

Same springs as my F450. 2800# will squat about 2.5", where the overload springs contact. Once on the overloads, our spring rate is 1200# per inch on each side, or 2400#/inch. 2200# more should squat about one more inch. My estimate for a 5000# load is 3.5" squat (+- 1/2")

 

The amount of payload on your sticker will not impact how much your truck squats. Assuming you are comparing two F350 DRW trucks, having a higher paylod doesn't mean your truck is physically capable of carrying more, it means it weighs less. The suspensions are identical and will squat equally under the same load.

 

Put air bags on the rear, and you can adjust the amount of sag.
if you do add airbags, I recomend upper stable load too. That gets 3 springs working together. The main leafs, the upper auxiliary leaf springs, and the air bags.
I have a Eagle Cap 1200. It adds close to 6,000lbs to the truck (all on the rear axle). I do not know how much it sags, but at 60psi in the bags with upper stableloads, the truck sits level, and handles well.

 

 

Stable-Loads engage your overload springs sooner under load. For the best info go to torklift.com. They don't engage when empty (on my truck) so they don't affect the ride quality.

 

Air bags are a must for that kind of load. You'll be so much more comfortable.

 

I didn't measure, but when I put my 5er behind my truck, it barely touched the overloads.
My empty pin weight is 2800lbs.
My loaded pin weight is 3600lbs.
I will measure when I get a full load.