I was (am) making a magic item, a +10 magic scimitar of Slaying [priests of specific evil deity]. It's going to have intelligence and a Will stat, and in looking through my RM2 books I find there's little guidance on the level of enchantment for Slaying - much of it is conflicting or (to me) illogical. In the opening pages about magic and equipment, ChL suggests a flat "slaying" ability and cost formula. Spell Law doesn't include any spells to make a weapon Slaying. RCI has some suggestions for Slaying spells of various types (5.5 Special Weapons Characteristics, p. 57-58) but the relationship between level and what the spell slays is unclear - it sort of corresponds to creature level, but not entirely.
Have you made Slaying ability a spell, and if so, what level or levels did you use?