Tile sizes in Blender renders are a big deal.
For CPU rendering 16x16
For GPU rendering 256x256
I had to downgrade Windows back to 8.1. Samplitude hated looking for VST folders and Premiere hated the video drivers on my Mac-with-Windows on it.
I think Blender hates the AMD drivers on the powerful Mac and I can't really upgrade because it's a Bootcamp computer. Bleh. It's hard to be me. So at the studio I have to use CPU rendering. That said, it's now vastly faster because I've set the tile size to 16x16.
At home I have a PC with a Quadro 4000 card and we'll see what happens when I set that to 256x256. It'll generate a whole lot of heat, that's for sure.