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.
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.