The poorer a graphics card, the more load that dumps onto the CPU, too, though. So that's for sure. That, plus the various changes of older bus speeds simply do make a pretty massive difference. A clock speed benchmark for what a game's system requirements are is really pretty meaningless once you go back past a certain point, even if the clock speeds are inline. That's unfortunate and frustrating both for consumers and for those of us trying to actually label our products with a clock speed.