In my opinion the stiffness difference between the 314 and the Z is not that big.
The deflection difference is bigger - the Z shaft, i would say, has app 20 to 25 percent lesser deflection.
But as i played pool for app. a decade before changing to 314 shafts, the Z shaft would be terrible for me.
The Z has a "European Taper" - i think that´s the way you call it in the US

It´s like a Snooker or Carambol Cue, it´s CONICAL from start to end, so starting at the ferrule, i mean.
I hate that feeling when i swing the cue and when i stroke.
The wood is going fater that early

That in my eyes is the biggest difference between the two shafts from a player standpoint.
Yes, the Z is a little bit "stiffer", and has "lesser" deflection then the 314, but that´s not the point.
It´s not that big of a difference in my eyes, but the big difference for me is that
conical taper - Weah !!

Hope i could help with my opinion,
Erich