So this is your own art; it seems official art to me. For those who don't know, Exar Kun was a master duellist in his time; he was a master of Form VI: Niman, the jack-of-all-trades style that emphasized moderation. Usually, a Niman practitioner is just competent, with rather relaxed bladework and unable to be a powerful duellist, but if someone really trains hard and is really a skilled swordsman, like Kun, then you are a master of everything; fast, strong, agile and precise all in one. However, Kun completely ignored all of Niman's ideals of moderation and instead fought with a Juyo-like fury. I must say that he is one cool and powerful Sith Lord; he'd give Vader a run for his money.
Well, in terms of lightsaber combat, I think post-Mustafar Vader and Kun are equals, but in terms of Force abilities, Kun has the edge, as he can do things Vader cannot hope to properly protect himself against.