Brendan,
Go the smaller, crappy tyres.
Oran Park skid pan isnt the words best...concrete is all uneven, gets bumpy and some of these exercises will be very stressfull on tyres.
the watering system...if you can call it that, doesnt do much of a job.
there will bemany dry patches, esp if they dont use the two water trucks...some of the parts of the pan that are wet, are on braking and turn in parts - makes it more trickier
Last day I was there for a motokharna, I chewed up my tyres from handbrake turns to power sliding the whole pan. there is nothing left on those tyres!!!and if I do this day - I'll be using one of my many spares I have