A or B spec?
I'm presuming A spec, you'll have to watch out for 2 cars, the Amuse GT1 turbo and the Audi R8 LMS '09 (GT3) car.
I beat the Audi by a few minutes with regular 8:15-25's, I think the Amuse is quicker though because it weighs alot less, but I didn't use a massively overpowered car, I tried for something a bit more competitive.
You'll either get the Audi or the Amuse, I did it twice and got one of each in each race.
There's a big thread on this race, if you can find that there's loads of suggestions for competitive cars if that's what you're looking for. 👍
If you want an easy win, just use anything with more power and less weight than the Amuse.