First of all let me preface this with I am not a fit expert but I own and have owned many bikes over the years and as you might have guessed several Cervelo's . I also owned a 2009 Cannondale Synapse. I am 178 cm tall so it does not directly translate to your experience but speaking from experience the numbers you are quoting from the sites you have plugged into do not appear correct to me. All the Cervelo's I have owned except my time trial bikes have been 56 cm and they fit me perfectly. You are 17 cm taller than me so my first thought would be that a 61 would be the proper size for you.

As I said I am not a fit expert and as others have recommended I would recommend getting someone who is to fit you. I just wanted to let you know I do not feel the online calculators are serving you very well.

The last thing , actually really the biggest reason I responded to this thread, is a warning. Make certain that when you or someone else cuts your seatpost if you keep the bike be absolutely certain that the when the seatposft is cut to make sure it is chamfered on the side toward the seat tube. Many S5's were ruined by the seatpost hitting the wheel cut out and permanently damaging the frame. Let me know if you need any more description of this.