1) Adjustable front and rear downforce. More than what you can get in other ways. In case of the front downforce, loads more. Like, +30 to downforce.
2) The car will be lighter than what you could achieve with a stage 3 weight reduction (which, in and off itself, is, what, 30'000Cr.?).
3) Racing exhaust, adjustable transmission, racing suspension and a few other things are being fitted as well.
4) Equps the car with hard sport tyres.
As far as performance goes, RM'ing a car is single best bang for your buck upgrade available.