Probably talking 70-75c (overclocked) max to be on the safe side, though the cpu doesn't throttle till around 85c.
Near sure i think intel reccomended a max of 65c, dunno what brand of crack they were smoking when they came up with that number, especially for the stock cooler. For some odd reason i doubt the 2.66 versions of the quad would be able to stay at 65c loaded with the intel stock cooler.