If you want a short bed truck, the 855S will work fine on a SRW. Truck camper magazine ran a nice article on keeping their 855S under GVWR with a SRW crew cab gasser. No way you will be able to do that with the AF811. My AF 990 is right at about 4,600 lbs wet. I wouldn't feel comfortable with the AF 990 on a SRW, but the Arctic Fox people told me that about 1/2 of the people who buy them run a SRW truck, so it just depends on your comfort level. I think the 811 is only a couple hundred lbs less, so pretty much the same thing, and again many people do it.
By the way, I am running a 3.73 axle ratio on my 2012 F350 6.2 DRW gasser and am very happy with it. There seems to be a common feeling that hauling a 5,000 load requires a higher axle ratio. I did the research and went looking specifically for a 3.73 in order to maximize my gas mileage. I'm really happy I went with the 3.73. With a 6 speed trans, there are plenty of gears for the truck to choose if it needs them. 90+ % of the time it runs in 6th, which is about 1550 rpm at 65 MPH. It of course shifts down on hills, but that's what the gears are for. I wasn't aware that final drive ratio affects payload on the SRW though. Are you sure about that? I thought it just affects towing capacity, not payload.
