9k is a pretty great way to go, for me at least. much prefer to the pants i have which were old taklas. not very high end taklas so maybe a really nice pro stock pant will be better than the 9k but i love the way the 9k girdle feels, i don't notice the girdle at all. the 9k girdle is a better design than the others i have tried. i specifically like the way the shell attaches to the girdle and the way the midsection of the girdle is form-fitting but the leg pads float. i think a 9k girdle protects really well because it's attached to your body and can't move, so you never get than thing if you fall and the pant shifts. but a pro stock pant might have better protection just because the outer layer of the pant is floating off your body and even on areas where there's no pads, there's still something there. with a 9k or any other shell/girdle combo, in certain areas you might have only the thin layer of shell.
i've never noticed issue of feeling constrained by a 9k girdle/shell, they fit very well and move with you. if you're heavy in the middle a 9k girdle isn't a good option i don't think, i can't see it fitting a beer-gutted body very well, whereas a pant will conform fine if you're big in the middle.