If it helps anyone thinking on this upgrade I'd really recommend this mod. I've gone the similar route to RR on my Ed30.
Recently bought a 4 pot set up for the front and decided to get the S3 rear upgrade too.
We had a slight issue when fitting the fronts (wrong fittings on the lines) so for about a week was running standard very worn fronts and the S3 set up with new/cheap Ferodo pads at the rear.
I found it made a noticeable and positive difference to the car that week, and now with the 4 pots on the front it stops really superbly.
Got mine (rears) off the For Sale section on here and all they needed, more for my peace of mind was a set of pads.
As an aside I quite like the black rear brakes myself..