Typography & margins. Rather than the line length, which is typographically a more appropriate reference point, use the margin settings of word processors. When establishing a house style, you should consider that readability decreases when lines are either too short or too long. Readability reduces if the reader must move from line to line too often and finding the beginning of a line is ‘laborious’ because, supposedly, the eye cannot hold the beginning in sight whilst reading on to the end.
Furthermore the readability would improve by using a broader bottom and right margin.
The line of a contract clause should contain on average 13 to 16 words, or 60 to 75 characters (but not more than 90). This can be achieved by margins of 2.5 or 3 cm on A4 paper size. Consider a broader left margin in view of the fact that letters and agreements are often kept in a binder (tying the left side closed, as they are often also single side printed).