Wayne,

Rory McIlroy certainly has a pivot-compression swing style, which is your personal preference. I have no objection to that type of swing style, but I have never seen you provide a biomechanical, or mechanical, explanation as to why it is a better choice.

Consider this comparison between Rory McIlroy, Jason Day and Jordan Spieth - who are all superb ball-strikers.

Here are capture images of Rory McIlroy at P4, P5 and impact.

Image 1 is at the P4 position - I have drawn a blue line at the level of the top of his head to mark his head position.

Image 2 is at P5. I have drawn a red line at the level of the top of his head, which shows that it has dropped by many inches (4-6").

Image 3 is at impact. His head has nearly remained at the same level - despite the marked elevation of his left shoulder.

Here are capture images of Jason day at P4, P5 and impact.

Image 1 is at the P4 position - I have drawn a blue line at the level of the top of his head to mark his head position.

Image 2 is at P5. Note that his head has remained at the same level.

Image 3 is at impact. His head is still at the same level despite the marked elevation of his left shoulder.

Here are capture images of Jordan Spieth at P4, P5 and impact.

Image 1 is at the P4 position - I have drawn a blue line at the level of the top of his head to mark his head position.

Image 2 is at P5. I have drawn a red line at the level of the top of his head, which shows that it has dropped by a few inches (2-3").

Image 3 is at impact. His head has nearly remained at the same level - despite the marked elevation of his left shoulder.

Here are capture images of those three golfers' left shoulder motion between P4 and impact.

Image 1 shows that Rory's left shoulder moves slightly downwards, but mainly horizontally, between P4 and P5. Then his left shoulder moves mainly upwards between P5 and impact.

Image 2 shows that Jason's left shoulder moves horizontally between P4 and P5 with no downwards-component. Then his left shoulder moves mainly upwards between P5 and Impact.

Image 3 shows that Jordan's left shoulder  moves slightly downwards, but mainly horizontally, between P4 and P5. Then his left shoulder moves mainly upwards between P5 and impact.

Although Jason Day's left shoulder's motional path is different to Rory's, I know of no reason to prefer Rory's left shoulder motional path pattern over Jason's left shoulder motional path pattern.

Do you have a preference, and why?

Although you prefer the pivot-compression swing style of Rory's (in terms of its bobbing down-and-then-up motion), I don't know of any advantage it has over Jason Day's non-pivot compression swing style. Can you describe an advantage?

Interestingly, Rory McIlroy's rotary pelvic motion stalls at P6 as seen in this sequence of capture images.

Note that his pelvis stalls at P6 (image 4) and it doesn't continue to rotate counterclockwise between P6 and P8 (image 6).

I believe that I can now rationally explain why this pelvic stalling phenomenon happens - see Q&A number 3 in this review paper at http://perfectgolfswingreview.net/pelvicrotation.html

Jeff.