Whats can we do (/upgrade) to make this game run smoother with more cars?

Hello,

My brother loves beam NG for the fact that in "real life", wrecking cars is a big part of his life. There's no car-game that comes near the experience Beam NG has to offer and he wants to enjoy that to the fullest, and his aim is to get 10 cars running in beam NG on max settings without any trouble.

The thing is, I don't know what's left to upgrade, or which setting is really performance-killing and could turn the tide. Any feedback, suggestions, and/or tools to track down what might be the bottlekneck would be much appreciated.

The (custom) build system he has (without overclocking) is:
ASRock Z170 Extreme4
Intel® Core i5-9600K, 3,7 GHz (note: ordered, currently i5 6600k 3,3 ghz)
Corsair 4x8GB DDR-4 Vengeance 3000 C15 (note: ordered, currently Crucial Sport LT 2x8GB 2400 CL16)
Gainward GeForce GTX 1080 8GB GDDR5X
iiyama G-MASTER GB2888UHSU TN 28" 4K
m2 500GB WD Black (note: Ordered and will serve as main HDD for OS + beam NG)
Crucial MX300 - SSD - 525GB

Note: He has a lot of mods installed which might take some performance, a clean install will be done later this week.

 

Launch in safe mode and turn off dynamic reflections, that's about all I know to improve performance whilst still keeping decent graphics