Amd Volcanic Islands details

[boxleitnerb]

^ maybe tolerance. If it's 39.9 and 40.1 fps, it is basically the same. No two benchmark runs will give you the exact same result, there always is a (small) variance.
Additionally, if they run quiet mode first, then uber mode, the card could be warmer during the uber mode benchmarks which may influence results slightly:

idle: 32C
during first benchmark: 85C (card relatively cool in the beginning)
after first benchmark: 60C (a little cool down while changing the mode and starting the second benchmark)
during second benchmark: 94C (max temp target) -> throttling