Consequence of using both filevault and cloud encryption
On macOS, FileVault is encryption at rest so it’s designed to protect your files when the operating system isn’t operating. Just as you can see an email or text document once you log in and your password decrypts the drive, any apps can read clear versions of your files and send them to the cloud in the clear, print them in the clear. 

Having FileVault doesn’t make things slower or faster, so you can pretty much exclude that from your worries and plans about whatever cloud sharing service and program you select. 

That service will be fast or slow, secure or not on its own design and merits regardless of the status of FileVault.