If you are going that high up you probably would tilt it, but I would lower it if possible (in a perfect world).
Viewing Angle - Tilt or Flat Mount?
Anyone have a rule of thumb for determining need for tilt vs. flush mount? Mounting 50 inch plasma above a mantle - bottom will be about 5 feet off ground. Optimal viewing spot on a sofa is about 11 feet away. Other regular seating spots range from 8 to 14 feet. There will be no need to angle to one side or the other. Thanks