Here is a quote from an interesting read. Chuck Hawks Article has some food for thought
Bullet terminal performance
A factor that has become more and more prominent in discussions of killing power is the terminal performance of hunting bullets. Assuming a rifle of reasonably adequate caliber, selecting the right bullet for the job can play a big role in killing power. Big game should be hunted only with bullets designed for the purpose. Frangible varmint type bullets and FMJ military type bullets are unsuitable for any type of big game hunting, and are illegal in most jurisdictions.
The perfect game bullet should not expand so fast that it fails to reach the vitals of the game being hunted. Nor should it expand so slowly that it essentially drills straight through the animal, expending the majority of its energy on the landscape beyond the target. An ideal bullet should reach the animal's vitals and use the majority of its remaining energy destroying organs and tissue. Often such bullets will be found just beneath the hide on the off side of the carcass.
http://www.chuckhawks.com/rifle_killing_power.htm
He seems to think speed does effect bullet performance. I wonder if the XTP was made for 2000fps?
D