Progressive render is slow, its slow like Poser or in Blender, I tested several times that like with CPU only or with GPUs

You can check GPU usage in SIV64 or HWiNFO to see in more detail what GPU usage it is, during the progressive rendering although MSI Afterburner outputting 99% usage but in reality is something like 70-80% usage

With tile rendering its similar GPUs usage in my case is like 70-80% as max, seen only on few occasions higher GPU usage in 85%

Hope this helps

Thanks, Jura