G'day Mike, welcome to the nut farm.
Re your brakes, have a read of this:
http://www.autospeed.co.nz/cms/A_0645/article.html
Maybe you're getting little rear brake effort. Also given the rear brakes are inboard they do tend to suffer fade quickly because they are out of a cooling air stream and also pick up heat from the engine/exhaust via the tunnel.
There is a vented rear rotor kit available from Spiteri (sp) Jag in melbourne. You use the same calipers but insert a spacer which comes with the kit.
Hope this helps.
Cheers