Personally I run a stress test for 1 hour on each intermediate OC. If there's one I think I might want to stay on, I run it for 2 hours, and see how that goes for a week.
Currently I'm having problems with this stage though. Recently found out that OCZ memory doesn't seem to mesh well with Gigabyte motherboards.. Of course, this is the setup I have.
Got some new Corsair on the way though. I'll be trying again after that.