srixon z-star or bridgestone tour b330 rx
I do a few wedge bounces with each ball that I try to get a "feel" for them. The Z-Star was the softest of the Pro V1x, Taylor Made TP5, Callaway Hex (Chrome and Black). As far as the B-330 series I can't make an accurate comparison. I can definitely say that they are much softer than the e5, e6 and e7.
Sorry that I can't help any more.