I found these "rule-of-thumb" torque coefficient values for various bolt thread coatings right here on the fabulous internet:
Multiply the torque value by 0.75 when adding grease or oil to bolt threads. Multiply the torque value by 0.65 when adding an anti-seize compound. Multiply the torque value by 0.50 when adding gear oil, Never-Sieze, or Moly-Cote.
If you want exact torque coefficients for specific brands and compounds, get yourself a copy of "Handyman In-Your-Pocket" by Richard Young and Thomas Glover (Sequoia Publishing). It's a nice compilation of figures and formulas for just about anything you'd want and more.