[JoshTriplett]

The workloads are determined by their customers, and customers don't always pick the exact size system they need (or there isn't always an option for the exact size system they need). The major clouds are going to upgrade and offer faster CPUs as an option, people are going to use that option, and some of their workloads will end up idling the CPU. Major cloud vendors almost certainly have statistics for "here's how much idle time we have, so here's approximately how much we'd save with lower power consumption on idle".