I've got access to 3 shafts for my poison cue (basically predator)
I have a Z2, 314-2 and the Venom Shaft.
The larger the diameter of your tip for the 314 & Venom shaft means that you have a larger striking point/surface of your tip making contact with the cue ball. This means that you have a larger margin for error.
The Z2 has a smaller tip diameter, which means a smaller contact point on the cue ball.
So you have to be more precise in where you deliver the cue through the cue ball - or else you may get too much, or not enough, and some times accidental spin (or english) on the cue ball.
Think of it like spinning a basketball on your palm vs spinning a basketball on 1 finger. You need to have that 1 finger in the right spot. But the palm... it's super easy.
A smaller tip diameter will magnify the error in your stroke. Watch a snooker player. They have 8-9mm tips compared to our 11-14mm tips. Their stroke is like clockwork.
It's actually really good to train with a training ball that looks like it has a spider web. It can show you exactly where you hit. Most of the time, you will not be hitting where your eyes think you're hitting the cue ball, and this is because the tip, and the cueball have curved surfaces. You will actually be hitting a little less than what you think. If you understand geometry then great. It's 750am here in .au and I haven't slept as I was out partying last night, and posting stuff on the forum, so I'm too tired to draw circles in paint/photoshop
This is my 2 cents on the different shafts, Hope this helps.
If you have a bullseye stroke, it shouldn't matter which one you use, it's all personal preference.
