I am running Sonar X2 and X3 on a Windows 8 computer. I am holding off on installing 8.1 Windows upgrade.
About all I alter in Windows these days is:
Select High-Performance Power Management Plan, then go into Advanced Settings and disable USB Selective Suspend, and also view/change Power Management Settings > Minimum Processor State and Maximum Processor State to both be set to 100%.
That's about it for what I change, as far as what comes to mind. IF it is a LAPTOP, I also disable the Wi-Fi transceiver prior to firing up Sonar, as those frequently REALLY spike system latency. This shouldn't be an issue on a desktop. (I actually have a USB Wi-Fi transceiver on my desktop, but it doesn't seem to adversely affect this computer's latency).
Edit - I also turn OFF all Windows sounds, as I don't believe anyone needs to hear those blaring through speakers.
Bob Bone