My FX-9590 and GTX 980 actually render slower in GPU+CPU than in just GPU 
I guess you have to have a high end CPU and a lower end GPU…
I got good results with smaller tiles, 64x64 for example.
Specs in signature.
Cheers, mib
What tile size?
if you get 8 threads of your CPU tangled up in some massive tiles, it could certainly reduce the render time.
A bit off topic, but for those after faster render times, Blender Guru posted a not often used tip on youtube today that decreases render times by as much as 48% in one of my scenes in 2.79
Would any of you please compare and test a cycles scene with the latest beta but enable “Simplify” in the “Scene” Properties tab and set “AO Bounces Render” to “3”? Hope it still works.
Really thinking that the ten euro a month I’ve been putting into the Blender Cloud for these last few years just has to be the best software investment I ever made.
2.79a is a bugfix release, the list of fixes that currently have made the cut can be found here also it will be build with cuda 8.61 not 9.0
Hi. People should know this about that feature:
and maybe all the discussion in that page on the subject.
About better render time comparing 2.79 vs master, this is one of the influencing factors:
https://developer.blender.org/D2766
https://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.80/Cycles#Optimizations
Ahh, cheers! 
I tried that, with GPU&CPU, tile size 32x32, my render time was 44.46, with that setting active, it was 43.51. Not exactly a huge difference. I have an Intel i3-4150 3.50Ghz cpu, 16GB of RAM and an EVGA Geforce GTX1050-ti 4GB.