If you go for a bicycle with a nearly horizontal top tube (ex.: Heron, Cannondale T-series or Trek 520), then I would go one size higher unless you have really short arms and torson and can't reach the handlebars). Also make sure the bike is sold with an uncut steerer tube and/or stem high enough to have your handlebars level with the saddle. Basically, I prefer to have the bike frame as large as possible. A higher bike frame is also more rigid when fully loaded than a lower one with more seattube exposed.

Now if you go for one with an oblique top tube, such as the Bruce Gordon, you will go for a slightly smaller size. Bruce Gordon provides a table with "equivalent top tube height", BTW.