Just thinking out load here (it's been a quiet night)
How much power is enough?

I know, I’ve read Mark Donohue’s gem "If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough horsepower" enough times, but how much really is enough?
So, what is the horsepower crossover point in a light weight, short wheelbase, front-mid engined car like a Cobra replica, where adding more power actually detracts from the driveability and maybe even makes the car slower for virtually everybody except a professional racing driver?
At what (HP) point does the knowledge that flooring it will just create lots of tyre smoke without a proportional amount of forward motion?
Cheers,
Glen