Well.. that's what i thought but AnandTech's review says different http://anandtech.com/casecooling/showdoc.aspx?i=3010&p=6
When overclocking with Intel Stock HSF c2D X6800 was only able to reach 2933mhz while overclocking with Intel Retail HSF, they were able to reach 3730mhz. There must be a lot of difference between those 2 HSF.
Edit, I got confused. According to Anandtech, the meaning of stock X6800 was the actual stock x6800 not a HSF.