Haven't looked at your files before now. Results with RealSR look fine, but are still on a blurrier side, which is especially noticeable on outlines. My solution uses ESRGAN with mostly the same models as Full 4K Upscale, which provides superb quality.
On original hardware it was even worse, about 4 hours for a single image when using ESRGAN fork in a mode that correctly preserves PNG transparency. I've rented a VPS for a month with a slightly better specs than my PC (sans the GPU), and with rebuilt PyTorch with Intel MKL support and other CPU optimizations it takes about 80-90 minutes to process a full bustup (768x768 image). As I'm writing this post, I've been running it for 72 hours, and it's halfway done with Ryuji. It is possible that I might obtain a CUDA-compatible GPU by the end of the month, if it won't be done by that moment.
In any case, my approach is pretty brute - take all GNF images, convert them, delete the blank images (which are just small white squares), process the rest, then just do a bulk replace of them all within this mod, without any changes to bustup tables themselves. Just to see if results would be bearable.