http://plaza.fi/muropaketti/tietoa-n...esta#kommentit it says that Nehalem clock frequency is determined by 133MHz reference clock frequency * multiplier. It's not ok to increase that reference clock since other systems are synchronized with that clock frequency and multipliers are locked upwards on regular Core i7-processors. Turbo mode works on regular models and can increase frequencies up 266MHz(2x133MHz). Turbo mode can be disabled from bios. Those EE (=Extra Expensive)-versions can overclock just fine and over 5GHz numbers could be reality.