I tried a lot of different settings I didn’t keep track of, however these are the best settings I found for my system:
CPU: Threadripper 1950x
GPU: GTX1080 Ti
OS: Windows 10 Pro
Best Times / Settings:
CPU: 51.92 secs / 8x8
GPU: 41.42 secs / 512x512
Just to note, switching around the ‘OpenSubdiv compute’ settings under User Preferences -> System didn’t really seem to have any effect on the times for GPU rendering. Not sure if that’s relevant or not, because I don’t exactly know how that setting works, but just wanted to throw that out there .
Edit: For my CPU, I changed the “Tile Order” to “Hilbert Spiral” and dropped the setting from 16x16 to 8x8, which shaved nearly 2 seconds off the render. Could make a sizeable difference when rendering an animation!