Bike size advice Bianchi vs Cannondale I have been after a Bianchi Via Nirone 7 for more than one month and an half without much success. The main reason is that they don't produce many 47cm frames, while 47cm would be my optimal size. 
In the meantime, I ordered also a Cannondale CAAD Optimo 48cm and it fits fine, it's arrived in the shop ready to be brought home. But I really want the Bianchi. The problem is that the cheapest 47cm upgrade that I can do with a Bianchi is the double of my budget (Sempre Pro). 
At this stage I'm very exhausted and temped to go for a via Nirone 7 50cm frame even if is going to be slightly too big for me. 
I already quickly tried the 50cm via Nirone and the hip isn't very stable, I do some small overstretch.
If I go for a 50cm frame I need to cut 2cm in the seatpost (seatpin). So, the saddle would be slightly lower than handlebar. 
However, watching the geometries of Bianchi Via Nirone 7 50cm and Cannondale CAAD Optimo 48cm I don't see much big difference. My leg inseam is 70cm and height is 159cm.
Bianchi Geometry:
 
Cannondale Geometry:

By the way, I did two 50 mile rides on Trek Domane, the first with a 47cm frame and the second with 50cm, and I felt more comfortable with 50cm. (But there wasn't any need of cutting the seatpost - I put it at the lowest position).
Trek Geometry:


Would would you do in my case? - Any advice?
When you buy a complete bicycle, you just need to check two things: fitting and components.

Did you test the 2 bikes in the size you are discussing? The Bianchi should have a better frame, but nothing that can counterbalance the fact that a 50cm frame is too big.

Regarding "If I go for a 50cm frame I need to cut 2cm in the seatpost (seatpin)" I would go as far as to say that you are voiding warranty and therefore it does not make sense to do so on a new bike. In my opinion, neither on a used one.