Darth Nox will comfortably destroy Cade Skywalker, IMO. The former wields combined might of several dark side entities/apparitions and is an absolute master of dark arts/sorcery. In short, too much for the Jedi to handle.
As far as Khem Val is concerned:-
Once a loyal servant of the Sith Lord Tulak Hord, Khem Val was placed in a stasis chamber in the tomb of Naga Sadow centuries ago by his master for safekeeping. Tulak Hord is long dead, but Khem Val lives on; a terrifying nightmare from the ancient past. Powerful, cunning and ruthless enough to slay even the strongest Force users, Khem Val was trained as an elite assassin. After emerging from his long slumber, the Dashade is the very embodiment of death and destruction; a reminder that there are things even Sith and Jedi must fear. Although once pledged to a life of service, with his original master gone, it is uncertain where Khem Val’s true loyalties now lie. A near-perfect killing machine, he could prove a valuable weapon for anyone willing to take him on… though he is a weapon that can cut both ways.
More information here: http://www.swtor.com/holonet/companions/khem-val