I shoot with a custom 12.25mm ob-1 and I tried the ob-2, a z-2, a 314-2, and a regular ob-1 at a local store last month. The ob-2 is stiffer than the ob-1. It gives you a little bit more feedback. You would get a lot of action from it, but it would hit a little softer than the z. I personally prefer the hit of the ob-2 to the hit of the z-2 because it's a little more "cushioned"... but I know people that prefer the z because it gives more feedback (you can feel the vibrations that go through the cue after a good hit with the predator shafts).
As far as your question - the ob-1 hits softer than the ob-2. Maybe a lot softer. The ob-2 is stiffer and gives you a little more feedback. One thing that I noticed when I was trying the ob-2 was that it is less whippy (because it is stiffer). My ob-1 is 12.25mm so the difference in the diameter is much smaller, but I can still see how the ob-2 can/would generate more action (because of the stiffness and the smaller diameter).
I shoot with a reduced ob-1 because I like that it has the most "cushioned" hit out of all the shafts that I've tried. With the ob-2 however you can "feel" the english that you put on the ball. You probably know what I am talking about, if you've switched back and fort between 13mm and 11.75mm shafts. You can't feel the english that you put on the cue ball with the ob-1 because the hit is too soft for that.
My opinion is that if you liked the z, you should go with the ob-2 and If you like an uber cushioned hit, you should go with a reduced ob-1.
St