Okay, I've had time to play with it and have double-checked all three settings.

For my board the roundtrip latency remained unchanged at "59" regardless of Standard, Turbo, or Extreme. All of the timings shown in CPU Tweaker remain unchanged as well.

I did a quick SuperPi 1M run, Standard and Extreme settings was 9.653 and 9.633 seconds respectively. Whatever setting it changes, it has a very minor impact now as compared to previous chipsets.