If a GPU says it's superclocked (an Evga term) or OC'ed or anything like that, the manufacturer has already overclocked the card. If it's $10 it's definitely worth it; not because you'll get a huge increase in performance (you will get an increase), but because the cooling is likely to be much better than the stock versions of the card.
If you are going to do an all-in-one liquid cooling system then it might be worth it to get the stock, because you will get excellent cooling and can OC the crap out of it, otherwise I never buy the stock cards.
J