Mix and match ram?

So I was curious.. let's say you have the Corsair Vengeance 64 GB ram sticks in the correct place and Corsair Dominator Titanium 64 GB ram in its correct place too? Will this work?.. like let's say every single spec is the same like speed and everything.

Does anything stop this from being optimal?.. wouldn't it just be the same as using 4, Corsair Vengeance 34 gb ram? Or 4 Corsair Dominator Titanium 34 gb ram?