Factory Overclocking

So how does the manufactures OC these cards example the 7800gtx cards 430/1200 but some manufact's set them as 490/1300 is it all a bio's thing....is any of the actual memmory changed voltage etc......

My BFG 7900gs that comes overclocked runs the same voltages as all other 7900gs's I've seen. The Overclocking is done in the BIOS.

all they do is find the cards that are good overclockers, flash them with slightly higher numbers and sell em for more... its quite easy to flash an nvidia gfx card bios.

im getting another 7800gtx that has a higher clock can i flash the bios to match it?? also my memmory chips on this Leadtek I have has 4 on one side of the card and 4 on the other most of the decent cooler look like are made for the them being on the same side how does the opposite side get cooled other than using heatsinks Im gonna be water cooling btw