You can achieve the same position on both bikes…there may be geometry differences between the two bikes, but nothing so significant that it means you can’t be in the same position on both (outside of perhaps some extreme examples).
ETA - meh, everyone else covered it. one of these days I am going to remember to read the rest of the thread before I hit “reply”. 
What are you doing with your Tarmac frame? Is it disc or rim brakes?
It’s a disc frame and I would most likely sell it.
Cheers everyone for the input👍🏻
I’ll play devil’s advocate here. Tarmac is perfectly good - no need to swap. The Venge is slightly faster. But you can close the gap to like 5 seconds over 40km or something if you add aero bars to your tarmac.
This is true and a whole lot cheaper. 
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Does anyone suggest a set of aero bars/stem combo.
Does anyone have the S-Works aero fly 2s and stem combo they can post pics?
I fitted aero bars to my tarmac, Pro vibe aero, as I could internally route the brake and di2 gear cables. These are brilliant bars, thinking of fitting to my other bike now
Did you use the standard specialized stem or change that also?
I’m planning to put an Aerofly 2 on my Tarmac, my LBS (Spec Concept Store) recommend upgrading to the S-Works SL stem but I’ll likely stick to the one that came with the bike as the S-Works only comes in a gloss finish and the rest of the cockpit is matt.
I’ll have to get a pic but I have the aero fly 2 on my tarmac with a zipp stem. Went with zipp since I needed a 140
Have a Fizik stem fitted but will be swapping that out to a pro vibe … I’m a compleshionist.
Not sure why folks think the black and white differentiator is whether you’ll be riding uphill or not. The difference between my SL6 frame/fork/seatpost and Venge frame/fork/seatpost was 42 grams. The difference in comfort was worth a fair bit more than that.
I’d say the choice is down to how good your roads are. If you live in an area with generally smooth asphalt (not a lot of road joints, rough chip seal, don’t ride gravel) - get the Venge. It does a great job of smoothing out minor buzz. Anything more - you’ll appreciate the Tarmac.
I recently swapped my build from the Tarmac to the Venge and decided to go back. I’m over the moon with that choice. And I’d have a hard time believing there’s more than maybe ~5w between the setups (considering I used the same bars and wheels)
P.S. The stack between the two bikes was exactly the same with the minimal required spacers on the Venge and both slammed on -12d stems
Which mount are you using for your Garmin? Trying to find a good one for my Tarmac (preferably with a GoPro mount too)
https://www.f3cycling.com/formmount
I am using this. I’ve got the aero fly 2 and the downside is you have limited options for mounting stuff on the bars.
I have them. In my Venge. That I got to replace my Tarmac. 
Granted, none was paid for after u was hot by a taxi… Aerofly bars are the shit. I love them. They’re comfortable and I like the dimpled top that give just a little bit of grip
Whenever you throw the Aerofly II on your tarmac I’d be interested in hearing about the process. My bar is showing up soon and I’ve never done any hydraulic/di2 routing before and am not sure if I want to try it myself or just have the shop do it.
My $.02…try it yourself. You have nothing to lose. If you can’t do it, just take it to the shop then. But if you succeed, you have learned a valuable new skill.
I’m planning on using the lockdown time to do just this…swapping out components in my CX bike and will try to do the brakes myself. If not, the shop is just up the street!
I’ll be taking it to the shop, I normally tinker myself but don’t have any hydraulic tools yet so will just get them to sort it.
Yeah, if you’re on the fence about doing the work yourself - don’t. Hydro is a bit more involved of a process. Though I find Shimano to be significantly less frustrating than SRAM.
