The GT World Championship pits you against top-class race cars like Le Mans Prototypes and Group C race cars. Even with a fully-tuned Black Edition GT-R, don't expect a win. You MUST fight fire with fire, use something like a 787B against the other Le Mans Prototypes such as the R10, R18 TDI, XJR-9, 908 HDI FAP, and so on.
I didn't have enough money for the 787B, so I tried a E93 M3 from Le Mans Series.
I used a fully tuned Buick Special and I won!