As an example, my undergraduate GPA was 2.65, and I obtained 990 on the physics GRE. The best undergraduate GPA in my school was 3.05, and the average GPA was 2.6
Actually, nobody can get a perfect 4.0 because teachers just give very long examinations which cannot be solved on time. In some cometitive examinations, I obtained 20/20 because they were rescaling the grades. Normally they give the exam, correct it and don't rescale anything (they don't give 20/20 for the best student). I know that it is stupid, but I cannot change the whole french system by my own.