FWIW, I'm of very similar dimensions and I can make either the 54 or 56 work for me but not the 58, since its effective top tube is way too long. As it is, with the 56, my stem has to be fairly short if I want to use drops. Unless you have the upper torso of a more primitive primate, or you like to be stretched out, the 56 will give you the more relaxed upper body position you say you seek but again this is just conjecture, go test ride and you will know.