OK Update with CPU and GPU modes with a target of 30fps my PC gets these results.
Instancing Spawning
CPU 21090 3110
GPU 22900 3160
Note that the main difference between the CPU and GPU Modes is when the framerate is tested.
In CPU Mode the framerate is tested constantly.
In GPU mode cubes are added then a inactive frame is allowed to generate the fps reading.
Very little difference and GPU mode spawning or instancing does not tax my GPU, I presume then the benchmark is CPU limited.
At least until DirectX 12 or OpenGL Next arrives!