Text Width and Margin Width Influences on Readability of GUIs
This study found ".. that, by itself, text width does not influence readability; however, there was a significant interaction between text width and margin width. The most efficiently read conditions were those with small text width (4-inch) and large margins, or the largest text width (8-inch) and no border. (1999-08-15)
The link address is: http://hubel.sfasu.edu/research/textmargin.html