It's not uncommon for my GTX 580 system to have consistently lower framerates in Skyrim, then consistently higher framerates. It really depends on whether you are out in the open world, inside, having a conversation, etc.
One thing to do is to play around with your Nvidia Control Panel "Program Settings" for skyrimlauncher.exe. The game graphics really do respond to override settings from the Control Panel. I had to turn down AA settings from 8x to 4x in the in-game Options, but then I went into the Control Panel and set AA at 8xCSAA, which seems to work pretty well. Set the Antialiasing Mode at "Enhance the application setting" and that should allow you to change the settings from within the Control Panel.
Absolutely turn off Vsync, and Triple Buffering only works in OpenGL games, so don't expect that to help in Skyrim.