After more tests I have finally come to the following conclusion. If you have a ton of cores on CPU, Firefly will most times give you the faster render time.

Firefly cannot really be compared to Superfly, as Superfly is a real ray-trace renderer and will always be slower.

Given the comparison between CPU and GPU on a complicated scene, the optix enabled render will always be the fastest.

Based on the image below, I have timed the following times

GPU optix 256 bucket: 343 sec

GPU optix 512 bucket: 331 sec - only saves 10 secs

CPU 128 bucket: 3469 sec

As can be seen GPU is 10 times faster! Total Vram usage 5.5GB

Elven castle is my own model imported into Poser. Ray traced reflections are well worth the effort.

My 1000W Corsair is not USB enabled. It is the cheaper version.