On a MBP15 2019 i9 2.4GHz with VEGA 20 / 32GB RAM.
The following settings were used to render the Nissan test scene.
CPU only 16 Threads.
32 x 32 Tiles.
Render time = 29 minutes.
And mold on the render. Especially in transparent areas. Even reflections of transparent areas.
The render should look like this (rendered on an RX 580) with the current RPR v2085.