What's the point of factory overclocked graphics cards?

They overclock the cards and thos settings are flashed in the BIOS. They normally offer better cooling to go with this and the warranty covers these overclocked settings. Sometimes the use faster ns RAM too. But yes, you can buy a normal card and overclock it yourself. Just read some reviews on various brands to see what one would have a good cooling solution that will let you overclock without aftermarket cooling. Most of the time its not worth the extra to get an overclocked card, especially not for 15mhz extra like some manufacturers offer. Rather than getting an overclocked version you better off just getting the next model up. If your motherboard is able to run crossfire you would be better off just getting another 5770.

Some factory overclocked cards are "cherry picked" for the best chips. Sometimes these will overclock better in some cases than standard bins. Mostly it is a way to financially exploit that all silicon is not equal.

hmm, ok. that gives me a better idea about it.
I'd still rather just get a more expensive card than wasting my money on some factory overclocked card that will be slower but almost the same price as the next step up.