Of course you dont want to hit 66 degrees celcius. While letting 65 degrees celcius be your limit. Nothing bad can happen to your system at 65 degrees, even 68 degrees celcius. But this apply's for experieced overclockers. Because obviously you want to push your system near its limit. So you can get every extra megahert. But only people that know what they are doing, can play safe by these rules.
So i agree with DJ, dont let your system get around 50 degrees celcius full load.
Finished With TF.