You're not looking hard enough. That's like saying 1 washington apple is better than another because it's bigger, when they're both good apples, one just exceeded your expectations. We always want to assume the apple's going to be a bit jucier than the average apple. We're all special and deserve better than the average (/end psych rant from crazy geek, no more posting while watching Criminal Minds!).
There's more factors to look into. In apples, it's the field, food, sun, etc. In memory, it's the IC used and the PCB (assuming the rest of the system isn't a limiting factor). Silicon yield is another factor, albeit either you'd have to do a LOT of surveys, or be a bad butt electrical engineer with a TON of expensive equipment to make that a real factor to even bother really thinking about.
You need to look at the part #, version #, and lot #. Posting that over @ the IC Inquiry thread @ the Corsair forum in the House of Help (LINK) will tell you the IC, which will give you a much better idea of why one OCs better than another. Of course there's always the X factor (dumb luck, bad silicon, etc).