Is there an easy way to predict where a line of text will break?

No. Where the text will break in a multiline text field depends upon on the font being used, where the text begins, the margins, the tab stops, whether columns are being used, and so on. There are many factors that affect where text wraps to the next line.

When using the Text Editor, you can control many of the factors that affect line wrapping, but when text is mapped in from an extract file, you have little control.