Well, I upscaled them at 3.5x, so got resolution of 812 pixels aprox. I'm currently using a P100 but when I was using the K80, upscale from 500pixels to 2K was not a problem.
Another matter is what you give to the VQGAN or MSE notebooks. For a K80 more than 500x500 is too much. For a T4 more than 600x600 is a crash, and P100 can bear 700x700.
What I would do is just upscale them, and then reduce the size in a edition program to match the max resolution that the GPU given can bear.