I tested out and compared the Z2, OB2, and OB Classic Pro last year. IMO, they were all pretty similar. OB Classic Pro played very similar to Z2, the OB2 had a more deadened feel, as it should based on construction.
If you like the 11.75 size and conical type taper, any of the three would be a decent shaft, if possible try to play with them to get a feel and make your decision.
Personally I might give the edge these days to OB based on feel and warranty, but I also used a Z2 for a few years and other than the need for replacements (which Predator took care of quickly) they were great shafts. I bet most people could switch between them easily with little impact to their game.
Scott