I have a question for you IVW:
I'm just a country boy with a little bit of bolt action experience, but I wouldn't call myself an expert. Why is it necessary to wrap the thumb on the firing hand to the left? Doesn't this slow cycling down? Does it assist recoil management that much? I leave my thumb to the right because it's heading there after the shot to cycle the action which I accomplish with the tip of my palm. I only wrap the thumb when it's not needed to cycle the action for the next shot.
Shooting a 500 Jeff with your thumb to the right hand side of the action(if you are right handed) would be interesting.
I have 4 rifles with the same action and I ques it is all muscle memory. As the safety gets moved back my thumb just keeps going to its normal position on the left of the action. I also do not use my fingers to cycle the bolt but rather the palm of my hand.