hard thing to pin down, what you ask.
however, if you've truly defined your positional needs then inspite of th general irrelevance of ST length, the larger frames usually have have more laid back seat-t angles; which, from your description, is something you're wishing to achieve.
Still, I recommend working with a well qualified fitter to define what you find to be 'best'. If you don;t already have some defined parameters, then getting a starting point is the cornerstone to finding a optimal fit.