Do we need to keep space under 80% on Power-Safe filesystem?

Do we need to keep space under 80% on QNX6’s Power-Safe filesystem?

On Solaris’s ZFS, to maintain performance, it is known as a good practice keeping pool space under 80%.

How to improve ZFS speed when the pool usage is 80% and above

Is this practice also valid for QNX6’s Power-Safe filesystem?

Both QNX6’s Power-Safe filesystem and ZFS are based on copy-on-write (COW) mechanism, so I’m assuming the Power-Safe filesystem has somewhat similar characteristics of ZFS. So, I tried to find a description mentioning this 80% rule for QNX’s Power-Safe filesystem, but, I couldn’t find it.

Is there anyone who has an experience on this matter?