I updated the Blender BMW test, so it would render a lot faster.
A new experimental add-on adjusts the so called “macho vertexes”.
And since BMW’s have lots of them, we can reduce a lot of time, but it doesnt work that well on a fiat 500.
Technical its complex math, however by performing such a pre-pass on the vertex model.
cycles can remove not necessary exaggerated surfaces and that reduces calculation time by 75%
Currently this python update is experimental beta, release maybe in Blender 2.83 (not 2.7x), its future is not sure.
Because today its just to hot to stay serious.