My PC SPECS:
GPU: Asus Titan X Pascal
CPU: i7 6950X - I overcocked it a bit.
Corsair DDR4 - 128GB
I was rendering in distributed mode with my another machine which has 6 cores i7.
Rendered images where from 3500px tp 6000px.
Render times were from 4-8h. Depending on DOF intensity. These were rendered as clean as possible because I had time and these images were used for my portfolio. So I needed the best quality I could get in a decent time ratio.
But if I would render these for production. I think I could easily cut that time in half. So 2-4 hours (for full hd even less than that). Also depends from the scene complexity. Simple scenes render a lot faster. Complicated ones with a lot of detail and reflections - takes longer.
Same story with every engine. I would jump on GPU rendering, but memory is a major issue.
I would not have time going and optimizing every model that would be so boring and insane :D I would rather create something beautiful in that time.
I think when gpu memory is going to become not an issue - 80% of us will jump on it. I would...
Good luck :)