Regarding GPU , I use corona for architecture exterior/interior .
day ago I've done livingroom interior for my client , rendered 1920x1080 in 17 minutes + denoiser
lots of lights and models, most of them with quite complicated shader trees (in other words not just textures with default settings) .
using 5820k/4300mhz . I don't need GPU at all
Corona is better than all other archviz and concept renderers