Not so long ago I rummaged through old images of Spanky at the Waybackmachine,
just to see if they had any original GIFs with embedded Fractint parameters
(since Noel Giffin didn't extract the latter when switching to PNG).

At the bottom of the Fractint deepzoom page are three (very) small images by
Minoru Morikawa with high magnifications I was able to get the GIFs from
(provided you need further test cases):

Those are great because they are over 1e300 and have comparison images. I tried the first two and they are so slow it will take a while to see it they work. The last one makes an image in about 30 sec with a very tiny window. There was a difference in a portion of the image so I need to see why.