...IME reducing the diameter of any alloy component like a stem or post goes pretty quickly, as long as you have already discarded the excess length on the bottom of the post. I woiuld be more like one of those "get the proper size" people on this one, though. I take a certain amount of comfort in having fouir or six inches of post down below the top tube juncture, because I'm a large person and the seat tube/post interface on my bikes takes a lot of weight bouncing around up there on top. I want a good, solid, slip fit for some distance along the post/frame tube interface. Not sure I can do that on something like a seatpost (turning it down accurately along the length of it.).