If you really want to enable all cores for compression and decompression, give pbzip2 a try. pigz isn't as parallel as pbzip2
*edit, as ac29 mentions below, just use zstdmt. In my quick testing it is approximately 8x faster than pbzip2 and gives better compression ratios. Wall clock time went from 41s to 3.5s for a 3.6GB tar of source, pdfs and images AND the resulting file was smaller.
megs
3781 test.tar
3041 test.tar.zstd (default compression 3, 3.5s)
3170 test.tar.bz2 (default compression, 8 threads, 40s)