The slidein pickup weight assumes you will carry a full load of people. The cargo weight will always be higher.
The Lance 650 is a small TC. I would call a 8 1/2 to 9 1/2 single slide to be moderate. I think you’d be better off going to see a lot of TCs of different sizes. Then, decide if you want to keep the current truck or not. My 9 1/2 double slide is huge compared to the 650.
I had a SRW with my current TC in my signature for over 8 years before no longer needing it for my daily driver. Actually, it was impossible even with a Supercab to park where I worked in Seattle. It was both too long and too tall.
Now, I have the F450 DRW. It’s obviously more stable heavily loaded even though we got by with the SRW. The difference was whether we pushed the weight or not. As is, we can bring whatever we want and are still under GVWR and have a lot more room in cab with the Crew Cab. Also, no problems when I pulled my wife’s Aunt/Uncles TT on a trip to Yellowstone about 1000 miles including the Rockies.
As far as driving the DRW goes, it’s pretty big. There are a few drivethroughs I can go through with the F450 because it turns so tight. I park at the end of the world even in the sticks or the “big” city of Missoula when I go there. Yeah, tiny city compared to Seattle. It’s a lot wider and that’s noticeable in parking lots or driving curves. I think it depends on how much you need to drive in town where it is busy if you’ll notice the difference with a DRW or not.