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On my 970 Strix card, 512 Tile size is the fastest. It cut the time from 30 seconds to 8 seconds.
With a tile size of 256 took a second longer for the scene.
You may also want to note that Blender Render will be gone in 2.8.
No Blender render in 2.8. I didn’t know. At least there is eevee.