As someone who use to practice a lot operating a bolt for quick shots, I can tell you the two fingers and thumb hold is not near as fast as the palm.  With the fingers/thumb hold you have to find the bolt, lift, pull back, push forward, push down.  It can be done quickly but with the palm the lift and pull back is one movement.  The push forward and down is a second motion.  There is no grasping or fooling around with fingers and thumb.  You have much more strength with the palm for cocking the bolt.  With the palm, you raise your hand with palm up and close with palm down.  

I always hated for some body who wanted a gun built to ask for a checkered bolt knob.  They look great but a custom checkered bolt knob can have sharp points on the checkering.  A smooth, round bolt is way better if you want to operate the bolt quickly.

Frank