I have no real hardware, though there is some assisted graphics. No options in Blender about Compute Devices or anything. I have quad core. See screenshot for spec.
128x128 Start Res ~120+ mins
16x16 Start Res 16 = ~28 mins
32x32 Start Res 32 = ~33 mins
8x8 start 8 = ~35 mins (stopped)
So the optimal for mine is 16x16 tiles with matching Start Resolution.