content: Unless i'm horribly midunderstanding the intent behind your analogy, I don't think you understand how CPUs work... If the amount the car can carry in that analogy is the so called 'difficulty' of the workload, then there is no difference between it and the 'speed.' If you are referring to IPC as the carryweight there, and clock as the speed, then you should know that, after the layers of software between you and the chip, a 10% improvement in one of those things means roughly the same performance increase as a 10% improvement in the other.