I think you lose about 300# of payload with a quad cab over regular
As far as raising the front end, I could only see that happening if you forget to open the tailgate or load is stuck to the bed. As the bed starts to rise you start dumping payload - by the time its at its highest point, its empty.
I have seen it happen though - boss' son always forgot to open the tailgate - had the big loaders push his front end back down all the time. Almost had it happen to me once - load of mud that froze overnight - enough came out to keep the front end from rising- but had to climb up the bed with a pick to knock it loose hoping I didn't go down with the load. And I didn't want to risk the truck by trying to lower it and having that weight slamming back down if I released the hyd pressure to fast