Nuge,
That' s the problem with understanding what equipment is appropriate for each set-up.......and I don' t mean to pick on you, I promise, but " Abouts" shouldn' t be acceptable when it comes to understanding your gear. The more you understand about how it works, why it works and what it will do , the more informed you can be about purchases such as broadheads.
I promise to do my best to give you good advice, I need some more info though, and the reason I ask is that the Spitfire is NOT the best choice for low speed/low KE set-ups. They open fairly slowly and have a fairly large cutting diameter that needs a good bit of energy to get he most out of them.

Carbon Express doesn' t make an arrow that weighs 13gr/inch? The highest is 12grs /inch and those are the Terminator HUNTER 6075' s
What are your arrows exactly? The difference between a 9.5gr/inch shaft and a 12gr/inch shaft is BIG when you get to the finished product.
Have you actually chronographed your bow or are you just guessing?