Would have liked to see the result, its maybe an edge case but i have a spacescene looping background, pretty fast, so compressing might have not been such an issue, also alpha is not needed, its probably best scenario for using jpg
the seperate jpg frames at 80% quality are smaller then 8bit png sheeted ones, and look pretty good, so i thought jpg sheeting might squeeze the filesize even more.
my results are for 24 frames using 510*510 texture
png lossless 10mb sheeted
8bit png 3,5mb sheeted
jpg 80% 1,4mb at 48 kb per image
I try an online test too see how it looks with the jpg