Sharepoint - Maximum Upload Speed to SharePoint Online?
I asked this exact question a while ago to MS Support. Their answer is you should expect a throughput of 0,75 GB/hour due to bandwith throttling, the CSOM, virusscanning, replication of data etc.
In practice you can reach higher speeds depending on the time of the day. 1 big file will also be processed faster than thousands of small files due to the HTTP-requests-overhead. Microsoft doesn't guarantee any performance on Office 365.
If you're trying to migrate (a lot of) data from on-premise to SharePoint on-line you might want to look into the Migration API:
- SharePoint Online Migration API User Guide
- SharePoint Online and OneDrive for Business Migration Speed