How much do GPUs generally overclock?

Hey all
I feel like I always hear that GPUs don't usually OC much past their stock clocks. This could be for a few reasons, including easier-to-hit thermal ceilings and binning of better-OCing boards for more expensive, factory-overclocked models.
How much do your GPUs overclock? How much is considered normal? Do different levels of GPU normally OC different amounts? I'd like to find out.
Is it strange that my EVGA standard 460 1gb is cruising along at 840mhz when the stock model is at 720 and the Superclocked one at 763?
 
Solution
There is no guarantee of overclock ability what so ever. Even from a family of gpu known good for OC, you can still land on a card with no OC headroom what so ever. It really depends on luck, the gpu lottery.
lol, in a laptop, NICE!
my old 8800gts OC'd from 500 core/1600 mem to 680 core 2000mhz mem on stock cooling. If you just google gtx460 overclock, you will see many, many threads about it and what people are able to achieve. Many people get the core to 900mhz on a 460.