@impiaaa@dev.glitch.social well my set up is:
GPU RX 480: tile size 512x512 about 8 seconds to render a specific scene
CPU Ryzen 5 1600: tile size 64x64 12 threads about 7 seconds

before i tweaked the tile size for gpu it was much slower but i guess that was the reason why

still, i was expecting a way bigger gain? idk