Paying Porsche a ridiculous amount of money for their coolant is fine if you don't trust what you read on the internet. But then I'm not sure why you'd be on the internet. There's no risk to using a like-formulated coolant at half the price of what the dealer charges. It's kind of like sticking with Mobile 1.
http://986forum.com/forums/showthread.php?t=9947&highlight=HOAT
According to toolpants, even the manufacturers know of equivalents.
http://www.renntech.org/forums/index.php?showtopic=3772&pid=18113&mode=threaded&start=#entry18113
G 05 is not compatible.