I hope what I am asking makes since.  At what differences do you notice MPF?  Also, is their a ceiling for MPF on noticeability?

For example, I play an AP2 with mpf of 508.  I used to play another iron that was 405, golf became a little easier for me when I made this change.  So a 100 point movement up I noticed.  Would you notice a difference between 508 to say 560?  What about 508-711?  Would you be able to notice the difference between your TS1 to the PTM?  With MPF, once you get to say 700, would you really see a difference if you went to 900?