VLC isn't very informative in it's playback speed designations.
Any idea as to which playback speed each adjective refers to?
Faster (fine): 1.1×
Slower (fine): 0.9×
Update: as of December 2017, neither "faster" or "slower" seems to produce a fixed amount of change in speed (for example, if one presses "faster" five times, the sequence of speeds it goes through are 1.5x, 2x, 3x, 4x, 8x, 16x).
Pressing [ to slow down and ] to speed up displays ±0.1 the previous speed as large text in the top right.