One thing the clown and castle images are also good for is to check how consistent the upscaling algo is in keeping line thinning roughly constant. E.g. if you look at the white van in the clown image, it has a stripe in the middle. Ideally an image upscaling algo should thin this stripe the same way from left to right. You can see in your upscaling result that the stripe is partially thinned very much and partially not thinned at all. For comparison, here's NGU:
NGU Sharp Low Quality:
NGU Sharp Very High Quality:
In Low Quality, the stripe is not thinned equally, either, and not thinned much at all. In Very High Quality, the result is not perfect, but quite ok.
Do you have good training images? If not, I can send you some nice ones.