Really depends on what torsion bars you have. If they're stock, you should probably use the process for setting ride height in the manual. If they're not, it depends on the wheel rate of the torsion bars you're using.
Also depends on the bumpstops. The factory "progressive" bumpstops can be a little closer, but if you've gone to poly button style stops you don't want to be contacting those all the time.
You can also check out this thread to see where some other folks are at for their settings...
