Actually for a G-Sync monitor, the fix is quite easy :

The engine does not like the higher refresh rates, so let's automatically use the one it wants !

1. Go to NVIDIA Control Panel
   
2. On the left panel, under 3D Settings select "Manage 3D Settings"
   
3. Once the main view has changed, switch tab to "Program Settings"
   
4. For now NVIDIA control panel does not autodetect Skyrim SE (may be it will in a future time) but if you found Skyrim SE in the list skip to 6.
   
5. Press the Add button, if you just launched Skyrim SE it should be on the top list. Else browse to the executable.
   
6. Now Skyrim SE should be on the dropdown list and selected. In the option list, search for "Prefered refresh rate" (not quite sure about the name, mine is not in English).
   
7. Select the "Controlled by the application" value instead of "The Highest" (which the skyrim engine does not seem to like).
   
8. On the bottom right of the NVIDIA control panel, hit "Apply"
   
9. You're all set :)

With this preset, my game never go higher than 52/53fps but never go below either : with g-sync enabled the game is perfectly fluid with all graphical options maxed out. Also the gpu just compute what's needed for the engine best refresh rate and therefor is a lot quieter.