The Q6600, being a 65nm CPU, is not prone to nearly as much error as its 45nm counterparts. With the "correct" TjMax, you should be showing reasonably accurate temperatures no matter which program you use. My preference is RealTemp though. Make sure you get the latest beta
which has TjMax set at 100C already, which is about what it should be. Come October 21, we'll know for sure.