Silva is a bit light for k1 I think. Machida wouldnt be good because karate doesnt work with heavy gloves.
I am not too sure about that mate, almost half of the K1 titles have been won by Karate fighters like seidokaikan and kyokushin styles.
Actually come to think of it apart from karate and muay thai, I cant think of any other style that has won it!!
Franklin,Gouveia,Maia,Kharitonov,Hunt,Liddell,Pari syan,Hardy,Shlemenko,Machida,Gomi,Bustamante,Evans ,Edgar,Hathaway,Bonnar,Murray,S.Carter,Ludwig,Pett is,K.Gill,Sobral,Mousasi,D.Cruz,Arona,Nogueiras,Co te,Ole Laursen,Kawajiri,Sakuraba & K1 Lebanner!