Height isn't likely going to be a good way to compare cockpit length between two bikes. I have a friend that is the same height as I am, but he's shorter legged and longer in the torso than I am. I bought my bike from him because it was the right size frame, but the first two mods I made were raising the seat up and putting on a shorter stem.
A set back post is going to move your weight rearward on the bike, as well as change your relationship to the pedals. A new seat post would likely cost just about as much as a new stem wouldn't it?