If you have a average chip, typically they will run at 4.0-4.2 at the high end.
Of course there are many variables. Some chips or golden ones will OC better than the average, and there are just plain bad overclockers that really dont want to be pushed no matter what.
Also, the quality of the motherboard has a big impact with the FSB type Ocing chips.
But in general, 4.0-4.2 is about average for these guys. If your getting more than that and stable, you have a good chip.
I ran my 9650 @ 3.6 for a very long time, even though it would run faster. Stayed there mainly because it ran there cool and right at stock volts. Was a good 24/7 clock I thought.