Depends. Setting the option to Turbo or Extreme tightens some hidden memory/northbridge timings and increases memory bandwidth quite substantially.
But if your memory is clocked to near its limit on the current timings (4-4-4-12/5-5-5-15/whatever) then Turbo and Extreme will start to cause instability a lot sooner than Standard.
so is it better to have the ram slower with turbo/extreme turned on?