It is really unfair to try to compare the Z2 to the i2. I have an i2 for my McDermott cue that I played with for years. I recently switched to a Predator (P3) with a 314-2 shaft and find I can easy switch between the 314-2 and i2 with minimal adjustment.
The Z2 is very similar to the OB2 shaft I recently acquired, however I hear the Z2 is often difficult to control; the spin applied to whitey is beyond belief and errors in tip placement are exaggerated significanly, so you have to be Spot-On with each shot or unexpected results with have you banging your head.
I have not played with the Z2, but talk with people who do...they often carry a 314 series shaft with them for those nights that they are alittle off.
Like I said, I love my i2 and my OB2. I have "shelved" my 314-2 for the time being because I cannot believe the improvement in my game since getting the OB2.
I hope this helps a little, I don't usually see responses on the Blogs. I might suggest posting this on the main forum (although I believe the topic has been debated to death and some posters may take offense to seeing the debate resurrected). You might want to use the search engine to find the existing threads for your analysis.