Taking into account an average driver and rider then imo you'd only need around 350-400 bhp to keep even the litre class sportbikes honest over the 0-60 dash..
It takes far more skill to launch the current crop of litre plus bikes to their full potential in a consistent manner compared to an M3 or RS3 with an auto box for example, however once out of the wheelie zone then the advantage falls firmly to the bike and it'll just clear off into the distance unless you are packing 650bhp + imo..
Bear in mind a BMW S1000r will cover 0-150 in 10.5 seconds which is only a few tenths slower over the same measure than a Veyron super sport with 1100bhp,
However this is all straight line stuff which is not only pretty boring but does give the bike an advantage, throw in some corners and the simple fact is that it takes huge cojones to pilot a bike to the same corner speeds as a car on the public highway, I have the scars to prove it