Train strength as high as you want. Higher hits are always welcome when PKing. :P Training range to 40 can be useful for green d-hide chaps and vambraces (no body, 40 defense and Dragon Slayer is required for that), or to higher levels for attacking. Magic can be used for binding (or teleports <_< >_>), or attack spells at higher levels. It really depends on what kind of pure you're going towards.