The FAA/Boeing approved AFM on the 777's and 747-4 at my company, state quite clearly that Turb mode has not been properly evaluated, and should be used only on a non interference basis. It goes on to state that WX mode is the proper mode for weather avoidance.
Having said that, and having pointed it out to Flt Ops/Safety and Standards, about 80% of our pilots still fly around with Turb selected for all operations. Go figure!
(ref AFM, Normal Operations, Weather Radar with turbulence mode)
Maui