The AC was an “update” to the X2, but is more like the next version of Castelli’s KISS chamois. Personally I think the X2 is far better (best pad I’ve used), it’s thicker, softer, and IMO feels much better on longer rides (similar to Assos). The AC is fairly firm and quite narrow in the taint.
FYI: I have a pair of last year’s CTT Aero Race bibs with the X2, and some of the same podiums you have.