As I suspected, XZ performs better at least for jquery. I was disappointed it was missing from benchmarks.

For comparison on my machine:

zopfli -i1000 takes [real, sys]=[1069ms, 21ms], 75730 bytes.

xz -9 takes [148ms, 15ms], 69476 bytes.

(Though as mentioned as a pro of zopfli, xz would lose on decompression speed for a larger file.)