I have a terrible luck with overclocking. I don't know if it's because I live in a hot country, but every time I tried to overclock any device I own, it becomes a unstable mess.
My QX6700 ran overclocked for most of it's life, but it was always too unstable/overheating all the time. It was an expensive processor, so I wanted to keep it alive on a secondary computer. However, it's no longer usable, even at stock speeds. It locks up and throws up errors every 15 minutes. I've replaced every single part of that computer, but that CPU is toast.
Every "superclock" (In other words, factory-overclocked) videocard I ever bought fried itself after 6-8 months.
My RaspberryPi, which has a built-in overclock feature, which you trigger via software, goes into a bootloop if I overclock it even the slightest.
I'm not taking chances with my i7 2600k. I bought a K because it was as expensive as the regular version, but I'm never touching it's multipliers.