My GPU has 6GB of memory, and my system has 32GB of memory. There probably isn’t any other single programme that uses more than 4GB of VRAM on my computer other than Blender. I read about that “Above 4G decoding” thing, but I do not exactly understand it. Do you think it would be helpful to enable it for Blender?
As I understand it the 4G decoding limits the ram buffer that the CPU can use to transfer data to the GPU. If you go above 4G then the buffer can be larger if needed. This means that the communication with the GPU will be faster, but also that you use more ram.
May be this option helps cycles to go out of core for example. It would be interesting to have a official reply from the blender team about this.
edit. For sure 4G decoding is necessary if you have multiple GPUs that’s common in mining rigs and professional rendering. So you have to enable 4G for “powerful” rigs to work fine. It is not mandatory if you only have one GPU.