I have Rigs of Rods as well on my system, which is very fast and can run the D line at 100 FPS.
On Rigs of Rods, I rarely get above 20 FPS.
Rigs of Rods only really uses 1 core (sometimes 2 depending on how it is feeling lol). I don't mean to bash the developers of ROR or anything but frankly it is very inefficient with CPU usage.