People already do that! The slower-speed versions of a particular chip are either chips that were flawed and had to be clocked down to work around the flaw, or

People already do that! The slower-speed versions of a particular chip are either chips that were flawed and had to be clocked down to work around the flaw, or perfectly good chips that have been clocked down to fill demand. Overclockers have been known to try to clock a "slower" chip to the speed of the high-end ones, and exchange the chip until they get one that works.