@Jempy Meanwhile, and until Peter gets back to you, if struggling with fps, you can start with completely disabling Extra FX. That should be, by far, the most taxing. On particles FX disable "Smoke (WIP, slow...)", it's a experimental feature under optimization.
If you get frame drops when there's smoke (or water spray on wet track mods), keep smoke at "minimum" on regular video settings, and disabling also "sort particles before drawing" and "draw shadows on particles" on particles fx
might help with draw calls. Some frames can be gained if you disable "Real Mirrors" (not to be confused with Smart mirrors) so the car interior isn't drawn on mirrors.
Ensure on regular video settings that you're not using a very high faces per plane setting on reflections nor max resolution for that.
Just for the RSS GT pack, you should also disable custom LOD settings ("Force low res..." under graphics adjustments), might eat some fps, but you can get glitches with the 57 with those options enabled.