I agree with some of the above but I don't think all of the info is correct.
I would rather have more braking than I need than not enough. Its easy to go fast but a lot harder to stop quick and uprated brakes are by far the best modification I have done to the S4 they instill much more confidence in the car.
The A4 is a heavy car esp once you have a full tank, couple of people in the car and the usual stuff we carry in the boot etc and thus take a lot to slow it down.
Yes I agree that the standard brakes are up to the job esp the S4's and will lock up the wheels BUT under repeated heavy use they can be found to be wanting and fade easily mainly due to excessive heat. This can be highlighed further if the car is tuned and driven hard BUT the standard brakes can be improved upon. Changing to EBC pads and grooved discs etc can go so far to improve things and the gains are usually small. One if the big problems with the A4 is the lack of brake cooling from the front if the car in to the wheel arches. I've seen standard brakes get so hot that the wheel bolts have come loose and a wheel come off a moving car!!
Big calipers with big pads, the RS6 pads have about twice the surface area of the standard S4 pads combined with big discs & big surface area vastly increase the amount of friction applied during breaking and under controlled breaking can dramatically shorten the stopping distance this does need to be combined with good tyes to be effective. The downside of more friction though is more heat and this is where the bigger discs really help by being able to disapate the heat much better, they generally are much thicker with bigger vents and either two peice or a floating design to prevent heat transfer to the hubs. Put a 390mm disc next to a 345mm disc and you'll see exactly what I mean.
I have Brembo 6pots and the standard S4 master cylinder works just fine. Yes the steering is a tad heavier with bigger discs but its not noticable and the gains in braking performance more than make up for it.
Never buy brakes on the way they look, they are functional and have one job to do in stopping the car and nothing should comprimise that!!
It all comes down to how you use the car and if you feel you need better braking. but I've never hear of anyone complaning their brakes are too good. Now if this is you route to work in the morning I would say your gonna need all the braking you can get
Italian side of the Stelvio Pass .........and yes it is as much fun as it looks to drive
