As far as I can tell, the three main differences are weight (~0.5 kg), that the Venge has a cleaner setup in the front (less external cables and integrated stem/handle bar), and that the Venge geometry and design is more suited to flater courses and the Tarmac more to hillier profiles.
I have never tried the Venge, but I prefer climbing oriented bikes (Cannondale Supersix > Systemsix, Canyon Ultimate > Aeroad, Bianchi Specialissima > Oltre), so it might not be surprising that I absolutely love my 2019 Tarmac. For the record, I prefer everestings to chain gang riding.
Depending on your preferences, one bike will be better suited to your needs that the other, but you won’t go wrong with either!
