Okay, I understand the first lot of images were not as good as they could have been.
But today I received this: One of your uploads has been deleted: 72p889 Reason: Low quality (visible pixels on background) Contact a staff member immediately if you believe this is an error. 9 hours ago
The image you referenced was a 3D car model rendered in 8k with an 8k HDRI. You state the 95MB HDRI was pixelated... I personally cannot see how this is possible, however, I will give you the benefit of the doubt.
Later I will upload the same model, but not use an 8k HDRI, I'll render the image in 8k as normal but swap out the 8k HDRI for a 16k version weighing in at 350Mb. I know there will be a slight difference because it will make FOV more clear. I cannot see the pixels and no one else has mentioned this matter to me.
Once I get a working version that is up to your standard, then I will know which HDRI's and the number of passes required.
I look forward to your reply!