I'd say, for running text, wrap somewhere before 80 characters per line (preferably before about 78, since some programs lose a column or two on display - personally, I wrap at column 72). I'm sure others will differ in various details, but I suspect most will probably be somewhere close to that.
If you don't wrap by 72, then there won't be room on the card for serial number, and it will be hard to reassemble a dropped deck.
