This is a screenshot of my best setup result.
No graphic mod, just Nvidia Freestyle.

Stable FPS @ 30.
Day and night.
Base map and map mod (even though I haven't tried all the map mods yet).
Default truck and truck mod (I use Scania by Eugene)

With default trailers and ownable trailer mod (I use Ekeri by Kast).
Fps rarely drops, only drops when an object requires more detail.