Abstract: Amdahl’s Law painted a bleak picture for large-scale computing. The implication was that parallelism was limited and therefore so was potential speedup. While Amdahl’s contribution was seminal and important, it drove others vested in parallel processing to define more clearly why large-scale systems are critical to our future and how they fundamentally provide opportunities for speedup beyond Amdahl’s predictions. In the early 2000s, much like Amdahl, we predicted dire consequences for large-scale systems due to power limits. While our early work was often dismissed, the implications were clear to some: power would ultimately limit performance. In this retrospective, we discuss how power-performance measurement and modeling at scale led to contributions that have driven server and supercomputer design for more than a decade. While the influence of these techniques is now indisputable, we discuss their connections, limits and additional research directions necessary to continue the performance gains our industry is accustomed to.