For example, I took my 16k square test image and saved it in gimp with 0 compression, resulting in a 1 GB file. This presumably applies the png filters, but skips deflate. Then I did this:

gzip -9:
57 MB, 59.8 s to save, 2.6 s to load.

zstd -18:
43 MB, 25.9 s to save, 0.28 s to load.

xz -9:
39 MB, 17.3 s to save, 0.48 s to load.