I just saw the Audi R8 GT3 doing a 1.59 around Bathurst. I did see that his top speeds on the straights where much higher than the same car in RR. I did try with the lowest wing settings and down the long straight in the last part of the track the real car was 20 km/t faster then the sim one.
Presumably you mean this video? The highlighted part is important. This means that restrictions usually put in place by series organisers to limit the car's performance have been removed.