I've had a Phenom II X4 965 for a year or so now, came clocked at 3.4GHz and I've overclocked it to 3.8, I tried 4.0GHz but had a crash so I geared it back and haven't dared go above 3.8 since. I have no idea if it was due to a lack of voltage, might be something I should look into 
I was just wondering, what is the highest you can realistically go with such a cpu on consumer-level cooling systems? I'm going to rule out the crazy ones involving liquid nitrogen and the like, I'm talking high-end aircoolers (I currently have a Noctua NH-D14 Dual Radiator and Fan as my cpu cooler) and liquid cooling systems.
Also, how much is the boost in speed worth it, and what kind of applications would the biggest effect be seen, if any?
I was just wondering, what is the highest you can realistically go with such a cpu on consumer-level cooling systems? I'm going to rule out the crazy ones involving liquid nitrogen and the like, I'm talking high-end aircoolers (I currently have a Noctua NH-D14 Dual Radiator and Fan as my cpu cooler) and liquid cooling systems.
Also, how much is the boost in speed worth it, and what kind of applications would the biggest effect be seen, if any?