UPDATE:
Pulled off the box (well I paid a pro this time, was lazy but glad I did).. turns out my NPC clutch looked as good as it did the day I put it on. We measured the disc it was about 0.04mm worn (which is nothing), both disc & pressure plate were in top notch. Had the pressure plate tested and the clamp was actually 1870 kg..
So why was it slipping you ask?
The previous owner had installed the incorrect bearing carrier so when the box was placed back onto the motor essentially the clutch was being ridden all day long ever so slightly.
So whilst the box was off, Scott from Western Clutch cleaned and inspected all my parts.. turns out ALSO my clutch fork was fractured.. lucky it never broke because that wouldn't have been fun.
Executive Decision Time
Since everything was off & being sorted, I told Scott I had issues going into gear on the track when I was in super dooper high RPM. He mentioned that the plates Doug used were heavy and when you press the clutch pedal to change gears, the inertia of the disc keeps the box spinning and hence it crunches when you select a new gear.. I bit the bullet and changed to a lighter custom carbotic plate.
At the same time, Scott modified my pressure plate, machined it and machined a step onto my fly wheel. He also replaced my bearing, bearing carrier (new), clutch fork (new) & spigot bush.
By the end of it, I now have a clutch that feels as light as a Yaris clutch (I'm not kidding either) with a clamp of 1700kg and no more crunching at high rpm shifts.
Sometimes it's actually worth paying a professional than doing it yourself.
Cheers & big thank you to Scott, his dad & team at Western Clutch at St Mary's
Now, anyone want to buy a 10" NPC Carbotic clutch disc that's nearly new? under 14 000 km old (3 track days, 1 skid day, and at the time car only had 200kW)