I've start test Houdini 18 and Arnold 6. the first test was simple splines rendering, 250.000 splines instanced 25 times. it loads a 140MB alembic file.
rendered in 6 core Xeon CPU and Nvidia Quadro RTX 5000.
the startup for Arnold GPU is slow, it renders faster, so its seems but for clear up the final image it takes for forever or just dropped /crashed, hard to tell on the GPU. the CPU is quite fast but much slower then GPU if it ever would finish. (adaptive sampling was on)
so far i am not impressed with the Arnold GPU rendering.
here the same scene on my MacBook in Arnold 5 CPU (no adaptive sampling)