I don't think you can get it so tight that the bearings wont turn ( I've never tried to ).
If my memory serves this morning... Preload is 5 lbs for used bearings and 7 lbs for new bearings.
Of course you can get it too tight until it won't spin at all.
Proper procedure is to tighten to 7-10 ft/lb while rotating, back off, and then finger tighten. Then back off whatever small amount it takes to install the castle nut & cotter pin. Most people just go by "feel" (and that seems to work too).