Windows 7: How much can I overclock?

How much can I overclock a Phenom II x4 965 Black Edition?
The heatsink/fan is the one which came with the processor, my case (Antec 902) has 3x120mm fans and 1x200mm fan.
The PSU is 600W
How much can I safely overclock this?

well..... the Phenom II X4 940 is good for 3.6-3.9ghz with good cooling, so yours has to be around the same or more.

these new phenoms clock far better than ANYTHING AMD have previously released, bringing them back into the OCing market with all guns blazing....

Unless the stock AMD heatsink/fan is a lot better than I recall, you want a third-party cooler for serious overclocking. (I'm using Intel at the moment; the Athlon 64 X2 was a few mainboard transplants ago.) I was able to use a rather tall HSF (Thermaltake Big Typhoon) in an Antec 900 without any trouble.

The big ones may require you to remove the motherboard from the case to fit a backing plate. In fact, that's a good thing: I suggest you avoid large sinks that don't require a backing plate. (Risk of it coming loose, or damaging the motherboard.)