I have some discus with a fairly large gold Severum and they all seem fine. Infact I even have a firemouth with them.. but to be fair it is a very placid one and never bothered any other fish (unlike some I have seen). I keep the water at 28c and 6.8ph
I think people need to clean the slate with the old info about discus. Things have changed a lot and discus are far hardier than they first were when you bought wild ones. If you get some of the fish bred in europe they can be pretty tough, and have been bred in water that is very hard with a ph as high as 7.8.
When I put some bloodworm in my tank it is the discus who are first in there and push the others out the way..