robow

I'm 5'10" and the 57 fits me well. It seems you likely have a shorter upper torso and longer legs similar to my anatomy. I'll bet you're looking at the 57 with a slightly shorter stem. The reach isn't that much greater than the 54 but the much shorter stack of the 54 will make it difficult to get you in the medium upright position you seek without a large angle upright stem. Unfortunately I'm told that the 520's now come with fork steerer tubes already cut and so you can't just leave it longer with a lot of spacers to get the stack you need. Best thing would be to find a Trek dealer and ride the two.