I’m sure this has been covered before, but I still need help.
The LBS has a good sale on limited sizes of Cervelo P3. A couple of years ago, I got sized up for a 55 cm QR. It seems slightly small to me but the 57 was likely too large. I’m 6’0".
The shop only has a 54 cm and no 56 cm models, but they said that Cervelo is sized slightly different and that it is more like a 55 cm QR. I’m a bit nervous that they are trying to put me on a bike because it is available, rather than that it being the right size.
Try it on and see how it fits you. Even better, take it out for a demo if they’ll allow you to. I’m 6’1" - 6’2" and ride a 55cm P3SL. But remember that it also depends on how steep or shallow you’d like to go. Going steeper shortens the effective top tube length. I’m right at 78° in the middle of my saddle and can get up to around 80° if I ride on the nose. Bottom line, it may or may not fit depending on how you ride, your dimensions and personal preferences.
I’m 6-2, and ride a 61cm road bike. I ride a 58 p3 for my tri-bike, and it fits me great. I was a little worried it would be to small before I got on it, but no problem at all.
I wouldn’t go just on this anecdotal evidence, but I think you might be surprised when you get on it. Good luck.
-Brian