Rate limit isn't respected correctly

I’m rate limiting the upload to 8750 KB/sec. That translates to 70mbps. Divide that by 8 gives you 8.75 MB/sec. That should be the MAX transfer speed. However the upload stays above 9.25 MB/sec for hours.

How do I get this rate limit to respect a true limit of 8.75 MB/sec or lower?

It is showing the logical transfer speed after taking compression and deduplication into account. You can use an OS-specific network monitoring tool to check if the actual raw speed is under the limit.