Do you have any possibility to try a Foil? I have a Foil and was recommended the S5, just talking faster bike. I think that if aero is really what it is you wonder about, why not check out a full aero instead of Foil or Venge? I will not ride Foil anymore myself. I did a long check up regarding frames and i do believe S5 is a good aero bike. But for me, i notice that if comfort is not good, it is more tough to ride for hours and hours. The small issues i had, grew larger as i did get more and more time in the saddle. I know a few using both S5 and R5 and they swear the S5 is the faster, but the R5 is more rider friendly. I have decided to go for a round tubed hybrid material bike. Titanium and carbon (Paduano racing Gladio). I have no clue or fact based answer, if this will make me slower or if i can keep my pace. I can tell you from the start i was dead-on that aero was the only bikes i was thinking of. But now i am in the belief that if i get best possible fit and comfort, i can push myself harder and feel better at the same time. Posture, technique, training etc is probably more important than blind belief of aero benefits.