Do you mean at 5K input (gpu render) the resulting image quality is better with the pimax 5K (native 5K res) than with the hardware upscaled image of the pimax 8K ?
Also my understanding is 6K input (gpu render) is the point at which the image quality of the pimax8K "begins" to become better than the pimax 5K (with native 5K input res), right ?
And optimal result with the pimax 8K would be achieved with a 8K input (gpu render), but then this is the same input requirement than the 8KX. In the eventuality you would have a gpu capable of rendering with good framerate at 8K why would you then use a pimax 8K which downsample at 5K in the middle instead of using a 8KX which would suffer no loss as there is no downscale in the middle ?
The only interest of the pimax 8K with its hardware scaler is then to be able to use between 6K and 8K input (gpu render) to offload gpu compared to 8KX requirement, as with the 8KX such an input res (= everything not 8K) should look worse as this is not scaled to the display native res.
But my concern is you seem to say the 8K image quality with an input of 5K is worst than the same input displayed by the pimax 5K. It was not the initial plan than the 8K would require at least a 6K input to perform better than the pimax 5K. I expected that with 5K input the pimax 8K would at least benefit from less SDE compared to the pimax 5K, with image detail level being on par with the pimax 5K (same input res = same detail level). You seem to say the hardware upscale in the pimax 8K doesn't perform good enough from 5K to 6K input to provide a better final image than the native 5K of the pimax 5K.