Don't exactly know, but when I'm stressing my VGA, the most it'll go is about 73°C. That's for my 7600GT, might be different with your 8600GT. The XXX edition is the Superclocked version, correct? Hmm, what you could do first before you RMA it is remove the fan, clean the stock thermal paste, and apply some AS5 or MX-1. Clean the stock thermal paste with some rubbing alcohol and coffee filters. I don't think it'll void the warranty.