GPU only: 10.9M samples/sec - 196 seconds for 1000 samples.
GPU+CPU: 11.2M samples/sec - 185 seconds for 1000 samples.
Samples/sec value starts lower, around 5-6M samples per sec, and progressively ramps up to these values.
Exported a .bcf and tried in LuxCoreUI:
GPU+CPU: 12.5M samples/sec - 166 seconds for 1000 samples.
Samples/sec value starts around 8-9 and then ramps up to 12.5M samples per sec.
It's sad that Blender seems to be slower than LuxCoreUI, maybe it would be good to have a "render in LuxCoreUI" button.
I guess it's correct then, it's a rather contrasted test scene so I can understand that it takes some time to render to acceptable noise levels.
Thanks for your help!