The recommended cargo weight for my Defender was somewhere around 2000 pounds stock.
It now has heavier springs, E-rated tires, etc so I'm not sure what the uprated weight rating would be. I'm guessing around 3000.
I've carried about 5000 pounds in it in a pinch, it only sank about an inch or so, but I was careful to stick to B roads and go very slow, as even though my truck has the optional factory upgrade of disks all the way around, the brakes are not really designed for that kind of load.
Ray