They are a bit laggy. Boost starts coming on slowly in the 3000-3500 range. 4000 it really starts to take off and hits full boost around 4600. So the acceleration effect is strongest between 4000-4600.
My neighbor said when I jammed on it he was thinking 'it feels kinda fast but not that fast' then it hit 4200rpms and his head hit the headrest :-)