Overclocking
We could overclock Core 2 Extreme X6800 from 2.93 GHz to 3.46 GHz easily. All you need is an enthusiast-friendly motherboard that allows to switch the multiplier from x12 to x13.
After increasing the core voltage we could boot the Core 2 Extreme test system at 3.73 GHz clock speed. It was, however, not stable enough to run all benchmarks.