AgreedFor someone who only gets about 30 days a year in, I'm not sure if I qualify to add to this thread, but I would have to agree, that the piston does not make this ski any better, or worse in the bumps. And I don't know how any "shop" guy would say the piston makes the ski "dive" in pow. Dive may be the wrong term. Float might be a better term, but again, it's not due to the piston. And speed also becomes a major factor of float.
Flex an unmounted AC-4 and then do the same w/one mounted. any noticable difference? Nope.
I have the 07 AC-4T's in a 177 and haven't really found this ski to be fantastic in the bumps, just as all the testers in all of the reviews. But man, at speed, does this ski ski or what!! That's when the pistons shine. Marker and Volkl did a ton of research in this setup, so I would be curious as to your findings if you remove the pistons. But my feel is that the AC4 is simply not soft enough to be considered a good ski for the bumps unless you are awesomly powerful.