The CPU can change power states in 10s of microseconds. If your core is constantly bouncing between C states expect it to add a couple hundred microseconds of latency. And if you have a modern linux kernel try disabling the intel_idle driver. intel_idle will disregard bios settings and very aggressively set the C state. This <i>kills</i> applications that high rps/low latency. I'd love to hear someone try and justify that behavior.