Neither am I - a fan of overclocking
with apologies for the use of the word fan, as that is your first consideration - an increased cooling requirement.
Overclocking means in basic terms over driving the components beyond the limits orignally set by the manufacturer
It is frequently risky to the health of the system, the life of the components that are overlcocked and indeed to other hardware, such as the fans.
So you may ask, as many have pondered the question, why do the manufacturers of the graphics, CPU, memory, even mention the possibility of overclocking.
The answer is consumer demand.
Ideally, with for instance the graphics, everyone would purchase, the particular GPU they wanted, for its intended use.
However in practice of course, most people tend to work to a budget.
Then the software writers introduce a new game, or a new version of a game, that performs better, on the slightly improved performance of a processor or GPU rated above theirs. Therefore the public demand is for hardware that can, or supposedly can be overclocked.
However if you research the manufacturers sites you will always find the cautionary warning such as
1. Warning: Altering clock frequency and/or voltage may: (i) reduce system stability and useful life of the system, processor, and other system components; (ii) cause the processor and other system components to fail; (iii) cause reductions in system performance; (iv) cause additional heat or other damage; and (v) affect system data integrity. Intel has not tested, and does not warranty, the operation of the processor beyond its specifications. Intel has not tested, and does not warranty, the operation of other system components beyond their industry standard specifications. Intel assumes no responsibility that the processor and other system components, including if used with altered clock frequencies and/or voltages, will be fit for any particular purpose.
Many graphics cards are sold already overclocked, from what the manufacturer of the GPU ie: Nvidia, AMD etc designed
Here for instance is the Diamond version of one of the cards you mentioned
The first video card we overclocked was the Diamond Multimedia Radeon HD 6870 XOC. This card was already factory overclocked,
so we weren't sure what to expect. We were shocked to see that we got another 105MHz out of the GPU Core Clock and exactly 100MHz extra from the memory. Reaching a core clock of 1045MHz was awesome to see, but we were disappointed with the memory performance. The memory on this card was the limiting factor in our overclock as anything over 1200MHz and we'd get freezes and stutters in games. <BR itxtNodeId="88">
Yours being the XFX
and from your Asus motherboard
Note4: The O.C. mode is not guaranteed. It depends on whole system configuration and other parameters.
Note5: For system stability, use more efficient memory cooling system to support a full memory load (4 DIMMs) when overclocking.
and returning to my opening remark about the fans, you can normally be assured that if you do overclock, you will require additional for the north and/ or south bridge chipsets, of the motherboard, sometimes the ram and certainly a perfect inflow/outflow airstream on the case, which must of course then be balanced, so that the cooler air coming in, is not then sucked out, at a rate, such that it simply passes through the case before achieivng its objective, neither of course do you want the airflow such that it stays in the case too long, eg the outflow cfm is too small.
Here is a very informative guide
In summary, the gain in performance is usually neglible and when measured against the risk of damage, the risk to the stability and life of many components, the extra cooling considerations etc, it is hardly worth that risk.