Well you do have or should have plenty of Ke to shoot the spitfires, I would guess your in the 65+ ft/lbs range. It really boils down to what is most important. field point accurcy and large wound channels, or better penetration, especially on bad hits or when you connect with bone. Both heads are very sharp and will shoot well with a properly tuned setup. Stingers will always leave a larger entrance wound and penetrate better. Spitfiires will be more accurate, and make a bigger wound channel, but won't penetrate nearly as well.