Yes, and very. A processor is always sold to be run at the rated speed, no higher. When a chip comes out of fab it is tested at extreme speeds and is slowly scaled backwards until a stable point is met. Then it is either rated at that stable speed, or downclocked further to meet a quota of specified speeds. For instance, if you buy a new 2.8ghz p4 today, it may have been cut from the exact same sheet of cpus that 3.6ghz chips were on, but it still might choke at 3.2ghz.