Specialized Venge v Shiv with same fit

I currently have a Specialized Venge, and I'm considering getting a TT bike so that I don't have to mess around with taking aero bars on and off and flipping the seat around a few times a week.

I was wondering though, aside from the convenience factor, would I be much/any faster over the HIM bike distance on the Shiv, given I can get into an optimum position for me on my Venge (I've had a BG fit) so I will be having the same fit setup on the Shiv.