By better or worse handling I assume you mean quicker versus slower, or twitchy versus steady.
Simply as a matter of calculating leverage moments, a shorter stem (especially with narrower bars) will produce a larger amount of rotation of the wheel for, say, a one inch movement by your arms at the outside edge of the bars than would the same amount of movement on a longer stem and wider bars.
Think of it like an "L" rotated to the right. The little end is the stem and the big end is one side of the bars. The bigger the "L", the farther away your control point (edge of bars) is from the pivot, and the less rotation for an given amount of movement.
That said, your dimensions sound about like mine. Same shoe size, 5'9", and a 31-32 inch inseam. My main ride is a 21" Trek 520 with a 50mm Nitto Technomic stem and 42cm Nitto Randonneur handlebars. I could probably use a 70 mm but it's okay as is. I have some toe overlap.
I suppose it is somewhat "twitchy". But with a set of loaded front panniers it rides like its on rails.
