Originally Posted by Hudson308

At 6' 1" the MB5 and Crossroads will be too small for you. The Hardrock may fit. Crossroads frames in your size will look like this. Notice the length/space at the back of the head tube. A good place to check with a quick glance to determine size on a vintage (horizontal top tube) steel bike.

Road bikes in your size will show 1.5 to 2x the amount of space shown at the back of the head tube. Of course this will always vary according to the geometry and proportions of a given frame, but it will at least give you a rough idea when perusing ads that don't give any dimensions.