If I have learned anything over the years participating on this forum, I have learned that on the question of up or down for framesize, there is no right answer. For example, I believe always size up. This is because more drop is generally less comfortable for the vast majority of riders. Further larger frames don't change as much in reach. Plus a taller head tube shortens reach on a larger bike...handlebars are closer to shoulder joints...reach is comprised of both horizontal and vertical components.
I see the mantra constantly of sizing down. I couldn't disagree more with this. I always size up.