Knockdown power is a myth, unless by that you meant % of one shot stops. Because the projectile exerts the same force (actually less depending on range), on what it hits, as it does into your hand in the form of recoil. I love my 1911's, but no way in hell is that recoil gonna knock me off my feet, dont get me wrong, i would go down, just not due to the sheer force of the bullet hitting me. However, in % of one shot stops, i beleive the leaders (excluding the big boys like .480 .454 .50AE and .500) are 10mm and .357 mag, edge slightly to 10mm.
/gogo