My Felt was a 54. I'm only 5'7", but it always felt a bit small. My Giant is a M/L and it says right on the sticker 5'10"-6'. It feels much more comfortable than the Felt and a lot more stable at higher speeds. I am however going to switch to a shorter stem. It has a 100 on there now, trying out an 80 today (that's one of those things that sounds like a lot, but it's only a 3/4in difference). The moral is to not get overly concerned about numbers. If it's comfortable, it fits.