Don't think a large is correct. This size sounds about right.
I am 5' 11 (and 3/4's, damnit). I have the M/L. The seat is jammed forward as much as possible and the stem as high and far back as possible.
It does fit pretty much perfect but, likely, with an M, it wouldn't be quite at the limit.
BTW, I also ride a Cervelo R3 and S3 in size 56.

Fair warning, though, highly recommended that you get a bike shop to dial you in. These bikes are not for the faint of heart--though they really deliver when dialed in.