Oh no, no, I'm not saying that they are bad because they are unstable. Note the part where I said it's price/value/stability.
That's what it's all about. You can get a system like that going for years, yeah... Heck, forget years, decades. But the amount of money you need to pour into it will be much higher than if you had bought a pre-built system with similar components.
1) Since it's a PC you built yourself, chances are you don't have warranty on the entire system as a whole. Now supposing you fried something and you still have the warranty, you still gotta pay shipping or repair fees or something like that or have to compromise something, unless you're dealing with a vendor who is completely perfect in that regard.
2) If it was a pre-built system then chances are you don't get to overclock or the overclocking support is very mediocre anyway, and if you open up the case to change components, you would void the warranty, and... either you run into the problem above, or you meet a company who is lenient enough to let it go and repair the computer for you anyway, but again, with a fee applied.
3) Supposing you made it this far without a single hiccup/error/fault/BSOD/break/whatever... then look back at the cost of the components that you had to add to keep it that way. Or if you're still using stock fans and stock components and it's rock-solid so far, you're probably one of the luckiest ones.
4) So you have a perfectly working overclocked system that does not require you to add anything exotic and falls into the perfect line, it doesn't mean that other people do, too. I mean... consider this: you yourself are thinking of adding another fan. It's that mentality that drives up the price of the system as a whole. Even if you do get a bit of performance out of the system, it'll just be about the same performance/price ratio as a pre-built system. Most often higher since you have to pay full price for softwares, unless you're toting Linux or something then... what was the point of running a Core 2 Quad on a Linux system in the first place if you're not a scientist working on a missile trajectory calculating program? Or assuming you did get it down to way below the price of a pre-built system using... "other means" such as promotions or cash backs or whatever, then again, I have to remind you that not everybody has it.
5) Reciting something again: just because you don't have issues doesn't mean other people don't have it.
Just because a group of... say... 1 millions don't have it doesn't mean the rest of the world doesn't. We don't have exact statistics, but what I do know is that you have more people complaining on forums about overclocking problems, RMA problems, and etc... than people announcing they got their perfect overclocking machine of dream.
And again, it's not just about the CPU, the RAM, your motherboard, or the stability of the system as a whole, it's about how much you have to pay, what you are getting out of it, and how long you can keep it going. That was what I meant. But I think you, and many others who are in the same class as you, looking for a system as high as one can afford, will just be upgrading before your system wears out anyway, so a stability test wouldn't be applicable. And then your old components will cover a portion of the cost for the new system, then you can go on with thinking that you got the faster and later and possibly better components of the generation until 2 or 3 more years coming. And that's just another thing. :innocent: You do get higher performance, but you pay more. Not that you'd notice it since you can make much more money in 2 or 3 years time.
Nowadays people don't buy a computer and be done with it anymore... Unlike back in the days, you buy a computer and you run it that way until your age has changed its tenth digit.