Why not google it for yourself? Here you'll get multiple answers from different opinions...that is quite a subjective question with multiple correct answers. Do you mean 0-60 MPH? 1/4 mile time? 0-120 time?....too many possibilities??
the fastest standard production model 4dr saloon is the cadilac CTS V there may be some modified holdens that are quicker though... try ford performance vehicles...
I think you are right with goin with the cadillac
it is the fastest around the ring (7:59) for a sedan but thats not always everything i like them as a cruiser too...