So I'm riding the P3c, but set up as a road bike for the technical nature of the courses I'll be riding.
Cervelo's top end aero road bike is currently the S5, which in many ways looks like the P3c. Curved seat tube being the most obvious example.
But I wanted to look at the geometry, to see how much they have in common fit-wise as well.
Cervelo P3c size 58
Head tube: 145mm
Top tube: 589mm
Head tube angle: 72.5 degrees
Stand over: 799mm
Seat tube angle: 75 degrees
Cervelo S5 size 58
Head tube: 181mm
Top tube: 581mm
Head tube angle: 73.5 degrees
Stand over: 791mm
Seat tube angle: 73 degrees
So there you go. The largest difference is the head tube length. I've compensated for this with a large stack of head tube spacers. Seat tube angle is a little more aggressive on the P3c, but this is okay because I'll be TTing on it and on the aerobars. Top tube length is nearly identical.