I've been riding a Trek 2100 in 54cm for the last thrirteen years. I just bought a 2004 model 2300 in 56cm. The bikes are almost identical in size. My LBS measured everything so that all the adjustments on the 2100 are duplicated on the 2300. The new bike feels a little different, but thats because the parts are shaped differently e.g. handlebars, brake hoods, saddle. After speding several hours on the web reading all the links suggested in this forum, I've come to the conclusion that if the bike feels comfortable, it fits, assuming that you can stand over the frame and that your position looks reasonable. If you are a racer looking for maximum performance, then all of the technical measurements may help, but for most of us, if it feels good it is good.