If you reduce the Voltage you'll get at least 10-15C drop... maybe the were fiddled who knows. Full chat on quadfire 7990's for me is around 85C tops... with voltage at 1.125v. At default 1.200v I hit around 96-100C.
Pain in the arse having to fart around with it, I'm tempted to take it apart and redo the thermal compound. If 90c plus seems to be the norm for retail cards on stock voltage something very dodgy was obviously going on with the review samples.