Nice to see you're using the same animation technique [1]. MP4 could not possibly provide this level of quality/size (~150KB per animation).
Pngcrush is rather limiting though. I could compress the PNG textures by ~8% more with optimage [2] (I'm the author).
And for newer browsers, serving the textures as brotli-compressed BMPs would actually make them >30% smaller (probably more with filtered but uncompressed PNGs).
[1] http://www.sublimetext.com/~jps/animated_gifs_the_hard_way.h...