I have played extensively with all 4 predator shafts, and the difference between the old and new generations is minimal. I believe the only changes for the new generation of either the 314 or the Z are the phenolic core that the insert is set into, and the new shorter ferrule made of the harder material. I guess the other change is the tip that comes standard, but I never use the standard tip. The tapers stayed the same. All of this is available on the predator website.
Here are my personal thoughts on the Z- The Z2 has slightly less deflection than the Z, but the difference is almost imperceptable. I do however notice that the resonance or feedback seems to be reduced by the phenolic core at the joint. I like how the new ferrule is less likely to scratch or get stained from chalk. My next shaft will be an unfinished Z2 that I will have a cuemaker put an insert into. This way I can have the better ferrule, but without the phenolic core. I agree that the Z shafts are very unforgiving about tip placement, and are not well suited for less experienced players.