X-Force is the fastest out there. But Ispoke with my local archery dealer and he said he won't even sell them, they have so much torque that you have to constantly have them in the shop for retuning. Not worth the money he said.
Speed does not make up for accuracy my friend, I would rather be shooting something that I know I will hit right on with then something that shoots 350FPS and might hit spot on one minute and then not the next.