One thing that wasn't mentioned is:
Right click on the desktop / Nvidia Control Panel / Manage 3D Settings / Check 'Global Settings' tab / Power Management should be on 'Adaptive'.
While still in Nvidia Control Panel: (Not that this step matters in BF3 - Just a check list)
Check 'Set Physx Configuration' / Under 'Select Physx Processor' is on 'AUTO'.
Tell me if that the first check list for Power Management is Adaptive and if it's not by selecting it, your GPU will go back up to 99% GPU Usage.
is all you need to monitor what your max GPU stats are after a bit of playing.
Good luck trouble shooting.