My body roll is kind of high with 250/300/no sway bar, 3" TTC arms and 30" tires. I do not do much in the way of high speed cornering.
Although I've never ridden in a stock P1000, so I don't have a lot to compare it to.
Since you haul a lot with it, heavier springs would probably be better. I don't know how much it'll change roll, though, and I don't know how the QS3 adjustment affects it.
We had a guy on here recently that was talking about going to 500lb springs for hauling a stretcher or something like that. I'll see if I can find him...