The --index option that I added (see another comment) to pigz allows random access so that uncompression could be multi-threaded. The workload I was interested

The --index option that I added (see another comment) to pigz allows random access so that uncompression could be multi-threaded. The workload I was interested in (compressing virtual machine memory during suspend) tends to be I/O bound. pigz struck a good balance to make it so that cpus and disks both stayed busy in an important subset of the machines of interest. This balanced saturation seemed to be optimal to minimize the suspend time. If the suspend image was on fast storage (that is, could saturate a 10 gig link) multi-threading uncompression for resume made a big difference. I tried pixz and I think pbzip2 and found that while the compress ratio was better than pigz offers, the delta in CPU-bound run time during compression was unacceptable. The scales may tip in favor of pixz when compression speed is less important than (e.g.) minimizing the amount of bandwidth required for 1000's of downloads of the compressed content.