Autocar tested the Senna vs 720S from 0-100mph-0 and these are the figures they got using launch control without roll-out. Clearly both cars got some wheelspin off the mark which is unavoidable unless you've got tyre warmers or smoke the tyres beforehand.
McLaren 720S McLaren Senna
0-30 1.60 sec 0-30 1.75 sec
0-60 2.98 sec 0-60 3.14 sec
0-100 5.53 sec 0-100 5.40 sec
100-0 4.13 sec 100-0 3.77 sec
So in the "real world" if you pulled up next to someone at the traffic lights and used launch control these are the type of figures you're going to get rather than some of the rubbish claims from other mags.
https://www.youtube.com/watch?v=nn8XerGldEk