I’ve did little test to compare Arnold refraction rendering vs Indigo renderer. since Arnold used spectral calculations for refraction, it was interesting to see how its sticks up to full spectral renderer like Indigo.
the render settings are fairly optimized for Arnold, Indigo gives not much room for optimizing. to be as fair as possible i use only pure the path tracer in Indigo. Anrold6 GPU is disappointed like always.
GPU was Nvidia quadro RTX 6000 with clockspeed at 1455 Mhz, the CPU was Intel XeonE-2276M at 2.8Ghz
2 minutes render time
it turns Arnold and specially ArnoldGPU is extremely bad with HDRi textures. with physical sky the times improved by the factor 3-6. with resolution limits on Hdri, Arnold gets a decent speed up, but Arnold GPU calculates forever on noises.