There are a lot more going on here than just the top tube and stem, really. The OP can also choose a bar that's short. The most important number he should be paying attention to is saddle to hoods (if he rides the hoods) distance after the saddle has been adjusted with correct offset from BB. Unfortunately all the geometry info Bianchi provided is not enough to dial that in, and it's probably something he has to do by trial and error over a period of time. My hunch is that he will be really stretched out with this frame with regular stem and handlebar. Given that, like a lot people already said here, why not starting with something in the middle of the range in term of frame size instead of going to the extreme larger end.