There is more than one way to overclock. Remember that clock speed is a function made out of both the reference clock (which is 200 for the FX chips) times the multiplier. So for instance 300 x 10 and 200 x 15 both give the same 3GHz. It used to be much more rare for CPU's to have multipliers that you could move higher, so most people overclocked by making the reference clock higher. The "problem" with that is that the reference clock also controls how fast the ram is going, so by overclocking your CPU, you were ALSO overclocking the ram. But if you are "multiplier" overclocking, then the ram doesn't change speeds at all (which is why I say your ram isn't the problem). So no, you don't have to be doing anything else to overclock.
And yes, when you overclock you DO want to have the lowest voltage that you can have (because of temperature reasons). BUT the computer also needs to be stable. So instead of thinking "highest clock speed, lowest voltage" you should be thinking "Highest clock speed stable with the lowest STABLE voltage". I apologize if I got you confused about that. As you can see, the most important thing about overclocking is remaining stable, otherwise all sorts of problems show up.
If it were me, I'd still do a few HDD tests just in case (short drive self test in seatools + SMART test at least). Just because a drive is new, doesn't mean it can't be bad, it just means that if it is bad, is usually under warranty