For every person who tells you should ride Aluminum, you can find another who tells you Steel is the only way to go (& probably there are people out there that say sell both & buy Carbon Fiber – LOL)
I agree to look at the fit first. Nothing is worse than a bike that is too big for you. And I would try to make your decision before you get your big training miles in for the ride. I am not a fan of making too many adjustments or switching to a new bike before a big ride / race. Comfort level is important & once you achieve that – run with it.
I guess I would ask who is taller? You or your son? Then put the taller person on the Bianchi.
And are you bored of your old bike? Do you want something new (or new to you)? If so, take the Bianchi.
Just my 2 cents.