Jim: "I'm not sure why anyone would choose anything other than an IAx series frame to be honest." (Granted, it was not in the context of P2 vs IAx.)

Tririg did their P2 vs. P5 with the current generation P2. The Cervelo P2 was my top choice going in to my bike purchase. But I could not find anything published that puts it in the top tier of bikes. It is always measured against bikes like the Felt B, lower end QR, Orbea Ordu, etc. The world leapfrogged the P2 since 2014; I would not be surprised if Cervelo introduces lower-end versions of their P5 design to compete.