I do think he was both a Powerhouse Sith Marudar and a Powerhouse Sith Assassin.
First his training was pure DS. So He cant take any of the Normal Jedi and Jedi Presitage classes.
if he was a Jedi knight, he would be a DS Jedi Guardian for his saber skills and Sith Assassin for his Sneak Attack.
He would be similar to my Guardian/Sith Assassin that both of them are very antisocial DSers.