The bike will handle exactly the same as before - each degree of rotation about the steering axis will bring exactly the same result as the old stem.
The difference will be in steering feel, and how much difference that may or may not make to you has so many factors it is i,possible to predict. You need to try it and see.
If its the riding position youre trying to make a little softer then 10mm will likely be noticeable, but how much is again dependent on all sorts of factors.