not exactly right but i get the point 
Heavier the vehicle , the more stopping power required. 
I meant all cars the same weight 
Put myself and Brad's car as an example. If we're both on the motorway and we both brake we're going to require the same stopping power, even though he's got 100hp more than me 
This is only accounting for a "freewheel situation" with the car in gear and breaking with the clutch engaged you will find Brads pads are going have more resitance from the engine therefore be under a lot more load. Brad has 100bhp more than std abf and I dare say at least twice the torque and maybe some more weight so he will need a high load friction material to be able to stop it while not burning up on those "Private road test sessions" at high speeds
The rear pads do very little work in comparison to fronts on both std and track cars, if your rear brakes lock up then you will find the back end is going the wrong way very quickly.
( A very good reason to not have sticky/siezed calipers on the rear of your car)
Even on non abs cars you will see a car in full skid with the fronts locked and the rears still spinning
This is why cars are biased with more stopping power to the front wheels (this is done via a valve or by feed diameter) so that they have more control under heavy braking or in a skid.
In a standard Mk3 Golf or any other Hatchback car of its ilk you will find the rear stopping power more than adequate for the car and very very difficult to glaze over or burn the friction material.
This is why uprated pads and discs on the rear of a normal car are more about kudos than actual improvement.
Trust me I have sat the exam got the certificate and built the hydraulic rig to test the friction material
The fronts however are a very different story
As said it is your choice and money all along and for £20 it aint gonna hurt is it
