Hello. I tested your cars on different tracks and there's my conclusion about these cars:
I like the stock version. It's pretty good car. I liked it's handling, breaking and even acceleration is decent.
And the tuner version is meh. I see no purpose on it, necause it has such amount of power, but it can't turn at all, also breaking sucks. This car can do 467 km/h, but that's all special about it. The only tracks it showed well on were long, straight grid map's tracks.