Well, I took the plunge and bought a box of Callaway i(s) balls, in white! I was expecting all sorts of good things; longer shots, huge amounts of backspin, ball dancing around the pin, etc, etc. WHAT A DISAPPOINTMENT! Here are my thoughts on the new (spin) ball.
I tried them with with both Ping Rapture (L48+) and Ping G10 (L59+) irons, the Rapture and TaylorMade R9 8.0 (L67+) drivers and the Z-satin wedges (L39+). Definitely got a few extra yards out of the drivers, but how much I couldn't say (as I couldn't replay the same shot with a different ball!). Although the G10's did manage to stop the ball a little quicker than the Raptures, the spin was so inconsistent with both sets of clubs and similarly with the wedges that I couldn't make a better score than I have with the ball I currently use, the GI3-S. I never got any ball to actually 'suck back' even with full backspin (even on Oakmont #2!!!), maybe not so surprising with the Raptures, but I expected some dancing with the G10's. There were times when I put full backspin on the ball and it still ran forward 10-20 yards (and it didn't land on a downslope!)
So, I guess they didn't work any better overall for me than the GI3-S balls as the extra few yards gained was not really of any benefit. And as the feel and durability of the Callaways is the same as the GI3-S's, the WGT ball definitely seems to be the better value ball for me.
Having read what other players have written about the new balls, I got to wondering whether something has been programmed into the balls to make them play differently for different tiers. I'm only a Master tier and was thinking maybe that was the reason I couldn't get the ball to spin back. I've just about used up all 3 balls and not once have I got the ball to spin back, even when ding'd.
Anyway, I've had my play, back to business now!