Not sure I agree on them being dynoed in 5th gear..? Although technically the most accurate, a run from low rpm would put car under huge strain accellerating from say 45mph to approx 150mph with no forward airflow over the rads, only what the fans blow!!
Not too safe IMO, I have always seen cars dynoed in 3rd on a 5 soeed and 4th in a 6 speed.