Hi Simon, this
website is probably the best about their products, as you will see they do several grades and I find the R-4S pad is ideal. JZ Machtech put me onto them years ago when I was dissatisfied with everything else we'd tried as they'd be using them on various race cars. I've not been able to find anywhere in the UK that sells them for a fair price (forget charging $=£, try trippling the price instead...), but there are plenty of US vendors and
EBS can do really cheap shipping if you're not in a rush, I try to buy in bulk from them as the savings are worthwhile.
I think the part numbers of the ones I use are:
For the front 250T calipers use AP372
For the rear 250T calipers use AP345
For the front of 944S/Lux use AP251
For the rear of 944S/Lux use AP252
A quick look on ebay will show you how cheaply they can be bought (£50-£80 plus carriage and vat), please do not be put off by the low price!
For anyone tempted to give them a go on the cheap I'd just start with doing the fronts, the extra work load on them will not overheat them, it will change the brake balance slightly of course but there's not much going through the rears on a standard setup anyway, I have done many trackdays and road miles like this over the years and find it to be no problem at all.