Improved air drag. Alot of gamestock cars in game if you take the governors off their top speed becomes absurd for example the etk 846-848-856 ttsport+ b become 210+mph cars and the ardente s410q frission become a 190+mph car.
I'm not saying the drag is wholly accurate to real-life, and there's a lot of room for improvement. But the ETK 846 has 502hp at 3627lbs, and it has a 7-speed transmission. A car like that could definitely hit 200+ mph. Go read around on some BMW forums, and see what some people have hit in their ungoverned M3s/M5s of the time. And you aerodynamicists and engineers can check the validity of the math and logic of this as well: