After a discussion in the forums I decided to add the option to override the settings of /sim/rendering on a per video adaptor basis (based on the principle used for joysticks):
viewtopic.php?f=42&t=28681&start=15#p275173
This code is now pushed to git.
The idea is to set optimal default rendering options for video cards so users get both good performance and decent rendering quality when starting FlightGear (for the first time).
Everyone is encouraged to add it's own personal configuration so first time users will get the best experience when starting FlightGear.
The filename is the OpenGL renderer string up to "/" (NVIDIA) or " (" (AMD/Ati) wit ".xml" appended.