I have owned a P3 since late 99 (that's last century), and I'm upgrading to a P3C. If I can replicate the exact fit and feel of my old steed, I'll be happy. Here's the thing. In the ancient days when i bought my existing P3, Gerard (aka, on this forum, God) personally looked after customer service, and pretty much everything else.
I emailed him my measurements (dress to the left, etc, etc) and he emailed me back (long since deleted - pity, I could sell it on ebay) and I THINK he said "you're a perfect fit for a 56 cm frame"
Anyway, I sent him $$$ and he went and personally made me a P3 on his mum's Pfaff sewing machine or something, and it did indeed fit perfectly.
Fast forward to today, and I'm buying online (I don't have the luxury of a LBS that stocks P3C) so before I part with many more $$$ I want to double check my size. Gerard no longer answers emails, not even from his mum (what have you done for me LATELY?) and even his Cervelo minions won't answer questions about sizing. So, I checked the charts on the website against my frame measurements, and this is what I get:
Front-centre is 610mm, just like a size 54 P3C
Stand over height is 765mm, almost same as size 54 P3C
Stack is 498, same as size 54 P3C
Reach is 435, close to size 56 P3C
Top tube is 585. I can't make sense of the Cervelo site on this, but that must correspond to a size 58(?)
My effective seat tube length is 490 centre to centre. Cervelo doesn't use this measure, but Tom Demerley's recent article (http://www.bikesportmichigan.com/reviews/cervelorP3Carbon.shtml) suggests this matches a 54.
Sounds like I've been on a 54 all along (I'm smaller than I thought) but it's ambiguous. Am I missing something?