Copied/pasted for the thousandth time:
Weeks, sSpecs and steppings are practically useless. This is because not every CPU from every stepping and week is overclocked, so it's impossible to know the best overall. People only know which ones seem to overclock the best. Overclocking is unpredictable because a CPU from a popular stepping/sSpec/week might overclock poorly, and likewise a CPU from an unpopular stepping/sSpec/week might do very well. Less than 5% of CPUs are actually overclocked, so no one can argue that one type overclocks more than another.
Another factor is user error. A certain CPU might be capable of 3.3GHz on air-cooling, but if the user isn't a very knowledgeable overclocker, or one or more of his components are sub-standard, he may only reach 3GHz. This user then decides to go on some forum and write about his "crappy stepping that only reaches 3GHz," when the fact is that the CPU is capable of more. This is why no stepping will guarantee a good overclock, or indicate the speed you will get. Every CPU is different, so the only way to find out how far you can overclock is to try it and see.
As time goes on, manufacturing techniques improve, which is why AMD and Intel are able to increase clock speeds. The engineering improvements from one stepping to a newer one is reason for the increase in overclocking potential. Some overclockers believe that steppings have some hidden meaning for overclocking, but that is just a myth.
Steppings have no affect on overclocking - they simply signify that some type of manufacturing refinement was made. Newer equals better in the overclocking world, but some ignorant overclockers like to argue that older steppings do better than newer ones. They base these theories off of only a few results, and fail to understand that truth that intelligent overclockers already know.
Some people even argue that some older production weeks are better than newer ones for overclocking. False! Newer CPUs based on the same stepping always have more potential than older ones due to the constant rate of improving technology. Weeks themselves do not indicate overclocking potential. I see so many false arguments like "week 31 is better then week 35, but worse than week 24." All you need to do to get the most overclocking potential is to simply buy a new CPU. If you can find a place to get a guaranteed week, great, that way you can simply choose the newest CPU possible. Just don't be fooled by myths that older weeks are better.
As a general rule, the newer the CPU, the more overclocking potential it has.