u/Laren_LR15

I am planning to build a WEC grid, and most of the cars are Ferraris and Aston Martins, specifically the Ferrari Vision Gran Turismo and Aston Martin Valkyrie. Since these cars are not in the GR.1 class, is there a significant performance difference compared to GR.1 cars? I understand that BOP applies only to vehicles of the same class [GR.1 GR.3, etc.].