$6k... spend it on, coilovers, strut braces, oil cooler, entry fees, brake pads, tyres, fuel and oil.
If you are hitting the track the biggest performance upgrade you can get is practice.
Unless you can lap as fast as Mark Skaife then I would suggest doing as little as possible to increase the engine power of what is already an old and powerful engine. Also the R32 is underbraked as it is, and you have to upgrade so many other things on it when you get more power.
Just remember that the car will be chewing through rotors, fuel and tyres.
Then keep saving until you have $20k and you can start having some fun