The percentage is relevant to the original BPM. 0.8% will have a varying degree of BPM change for say, 120 bpm and 125 bpm track. I do agree that 0.7/08% can be used as a rough guide, however, you will still need to use your ears/headphones to fine tune it like you say. Hence, my non-understanding of how anyone can beatmatch without headphones. Yeah of course but for genres that dont change too much in bpm like house and electro (which is how a steve angello set would go most likely staying at 128bpm) 125 - 132ish is all 0.8 per bpm give or take small differences, if you had edited tracks or perfect autocues set you could quite easily dj without headphones but you would be nudging the jog while people can hear it which isnt ideal