You set it to 100 manually to lock it there.Auto does not lock it.It will drift when you overclock from stock speeds.How far will it drift with auto?I have no idea.But you will probably just lock up the computer after awhile because the pcie went to high.But that's what the lock is for.So only the FSB goes up and not the pcie.You could probably even damage the video card if you ran it to high for a long enough amount of time.I always lock mine at 100 and don't seem to have any problems getting a high overclock.
:)