If you are building a "gaming pc" then I would suggest getting non ECC ram because the price premium paid for the error correction imho is not worth it. You will get a little more performance but not much. If you are building a server pc where stability is required then ecc is the way to go. But even without ecc in ram, most problems are caused elsewhere. As for overclocking, I havent heard of ecc ram helping in overclocking but get high quality non ecc ram ie. crucial or muskin and you should be fine.