What you are feeling
Slip usually shows on a hot clutch, in a high gear, when the revs rise and the road speed does not. A short test drive somewhere safe will tell you more than any noise from the pedal.
Check the fluid and the pedal free play before you blame the disc. A hydraulic fault can feel the same as a worn plate.
Matching the kit to the car
An R34 GT-R is not every R34. Confirm the year, the gearbox and whether the car already has an uprated plate before you pick a twin-plate kit.
Organic suits the road. Ceramic and multi-plate kits hold more torque and they are harsher. The catalogue lists the chassis on each kit. If the years do not match the car, stop and ask.
Before it is fitted
The flywheel, the release bearing and the alignment matter as much as the disc. A kit that includes the flywheel is the simpler order when the original face is heat-marked.
This is a buying guide, not a fitting manual. The installer still has to set the release travel the kit asks for.
More guides: Skyline blow-off valve choice · Choosing GT-R brake rotors