1 hr may not be stable, 3 hrs is were I fail most, 6hrs is good 12hrs is better. There are some great tips & guides here in this post written by some overclockers with lots of experience, follow what they wrote and you will have a solid stable OC.
Here is another on Prime95
Here is a tip I found somewhere here (can't find the link) in regards to using Prime95 and a starting point without running 3hrs to fail.
Set to custom set FFTs to Min-1344 & Max-1344 set ram to 80-90 percent of your ram (I have 8gig so I set it to 6500) set time to 1 minute if it passed 20-30 minutes I ran.
FFTs min-1792 & Max-1792 same ram & time for another 20 to 30 minutes, if all goes well than on to 12hrs blend with ram set the same.Edited by We Gone - 1/8/12 at 7:00pm