RE: 60# versus 70#...No difference in power? Maybe
Your comparing PSE's flagship to the lower end models of other companies.
See how the 58# Xforce stacks up against a 70# Elite GT-500, or a Bowtech 82nd Airborne...
Not saying the xforce isn't a great bow, just that your comparison is off...compare apples to oranges at least...not apples to cars. My 70# Hoyt Vectrix has an IBO of 316, but I am cranking over 80# of KE. That IBO is slow by the new speed bow standards.