This is most noticeable when im fighting WB.
My main character (conq) has far less FPS than my other toons, they have exactly the same video options and even then i fall under 5fps with him, when with the other im around 20 (vs a WB with no particles enabled)
funny thing is that, even when i put low video settings for this character, the fps stays the same... there is no impact to de fps at all even with the lowest graphics.
i apologize for my english.