Great stuff Drew! I have been mulling over posture-related stuff recently. I think I straighten my spine on the downstroke as a compensation for a spine angle that is too steep to begin with. Rereading Hogan's Five Modern Fundamentals I was taken back by the method hogan used to organize himself at address.
1. Stand erect.
2. Lower arms
3. Flex knees while keeping the spine erect
4. Bow head from the neck without hunching the shoulders.
The spine angle in his case is created by the out of line condition that exists between a straight spine and flexed knees.
Between the straight spine and flexed knees you cannot help but have a flat shoulder and hip turn, right? My point is that perhaps I am better served with a more "upright" torso posture as opposed to increasing the bend coming down?
On the pics of Hogan the degree of waistbend from a 7 iron to a driver is negligible. Not something I notices before. The amount of knee bend (obscured by tailored pants) and neck bend is what makes it look different at first glance. A lot of tour types stand tall.