Request: max width for better readability in Lion fullscreen

I’d like to set a max with for text display in Lion fullscreen (similar to the width preferences for DTP fullscreen).

Since I’m on Lion I find myself switching to fullscreen more often and I like the way DTP is doing it letting me concentrate on one (ore more) main windows. But the viewer pane becomes very wide in fullscreen and lines of text with more than ~70 characters are hard to read.

Preferably the width would be set in characters not in % or pixel. If you hesitate to introduce a new preferences option for this, why not simply set an internal width limit of ~70 characters (which is a bit more than what is considered best practice for readability).