Have you tried a heavy armor with some defense for higher levels on Samurai/Paladin? I notice a difference in defense with a non-ee plate rather than a robe or scale, and even more of a difference with a plate with EE on it. I am not sure how much the mpk/mpa/lpa assists at high levels, but you could easily gain a lot of defense and some intelligence, as well as other mods, by trying out a plate mail with int at higher levels.