Derklord |
You are indeed wrong, Mr. Charisma. "Spells that provide bonuses or penalties on attack rolls, damage rolls, saving throws, and other attributes usually do not stack with themselves." (CRB pg. 208)
Greater Bestow Curse is a different spell, though, so the effects do stack with those of the normal version. I'd say there are more nasty things to do to a target that fails its will save against both a 7th and 3rd level spell from you, especially when you're already in touch range, but I guess that's beside the point.
You could also stack Conditional Curse and Major Curse with them.