Axis/Oxyron released the source for his demo "Rock Lobster", it includes a packer/depacker that he claims "is unbelievable fast (about 180KB/s on a stock Amiga 500)" at depacking (and given his track record, there's no reason not to believe this). Includes C source for the packer and asm for the depacker:
https://github.com/AxisOxy/Planet-Rocklobster