Actually the monster has to be invincible (you must hit 389% of the time or less with rapier) for longsword to be better. This assumes 99 attack and strength; Neitiznot, fire cape, fury, rune defender, barrows gloves, dragon boots, onyx/warrior (i); with extremes and turmoil (29%/32%) held constant. This assumes you don't have to pause and eat, in which case slower, stronger weapons gain a slight advantage. EDIT: holdon them maths r rong