I’ve been working on these Blender courses using two computers, my work Surface Pro 4 with an i7-6650U processor with 2 cores @ 2.20 GHz and my personally built desktop at home which is running on an AMD Kaveri APU A10-7850K 12 Compute Cores - 4 CPU Cores + 8 Graphics Cores 3.7 Ghz Turbo Clock: 4 Ghz 4MB of Cache with Radeon R7 Graphics and 8GB of 2133 Mhz DDR3 RAM.
Obviously my Surface tablet is going to be running much slowly. I was also doing work while the renders ran.
at 128 Tiles it rendered the scene in 13:19.39
at 64 Tiles it rendered the scene in 13:37.43
256 Tiles rendered at 14:03.51
My Desktop seems to produce similar results. I didn’t really have time to try a bunch of renders. I’d start them and look at the estimated times.
512 Tiles for my AMD R7 GPU using OpenCL rendered at 13:33.89