Its not soo much in relation to how fast the speed catches up with you...rather if you modify your car (eg. take the speed limiter off) and are involved in an accident, even if you pay insurance the insurer may refuse to cover you. This may depend on whether you inform your insurer of the modifications made to the mechanics of the car..which im guessing they would need to / or should know about given how anal they are about items fixed to your car.
Furthermore charges could be applied should you be deemed to have modified the car to an extent that it is unroadworthy and hence driving an unroadworthy and unregistered vehicle which is an offence.
Nevertheless, each to their own....was just something of interest sake i guess more than anything.