gzip compression work unit size?

What value should the number of kilobyte chunks per compression work unit actually be? Backups regularly cause serious load spikes on a 24-core box with 32gb RAM that normally sits at a load average of 9.0--even with the compression level set below the default of 6, (4) and the number of simultaneous threads set to 1 (the default of 1/core makes me shudder)

cPanel documentation doesn't give any substantial information about how to set this value effectively other than including a default of 4096kb.

What would be the difference in recommended values between, say, a 4mb cache and a 40mb cache? What constitutes "larger" when the (?) mentions:

"Number of kilobyte chunks per compression work unit (Minimum: 128; Maximum: 524,288) [?]
The size (in 1024 byte chunks) of compression work units to be distributed to each pigz process. Default is 4096. Systems with larger L2/L3 caches may benefit from higher values."

Any advice would be welcome.