Hi Ken,
It all depends on the printing technique used (ie coated paper, output dpi, upres). Your printer should be able to answer these questions or better you change your printer.
I use Photokit sharpener when I am not doing the sharpening in Lightroom. Photokit sharpener has some output sharpening routines for halftone printing.
For example for Blurb books you resize the photo exactly to the size of the placeholder in the book and use output sharpening halftone coated 175/350 dpi. (Blurb presses are set to 175).
Hope this helps a bit.
Jaap
