GPU renders are quite slow on my rig and also slow down user interaction with Mac during rendering.
On the other side CPU rendering is, well…OK. Furthermore, I can read some article during the render or browsing some hardware e-shop and dreaming about kick-ass computer for my 3D career
Machine: iMac 27" Retina
CPU: Intel® Core™ i5-6500 CPU @ 3.20GHz
GPU: AMD Radeon R9 M390 2048 MB
OS: macOS Sierra 10.12.2
Tile size: 520x270
Time: 14 min 03 seconds (CPU - OpenCL)
Time: 13 min 26 seconds (CPU)
Time: 14 min 30 sec (GPU)
Tile size 260x135:
Time: 10 min 54 seconds (CPU)
Tile size 120x68:
Time: 10 min 23 seconds (CPU)
Tile size 60x34:
Time: 09 min 43 seconds (CPU)
Tile Size 30x17:
Time: 09 min 37 seconds (CPU)