Is OneDrive local as fast as C:?

If the drive that the OneDrive local folder is on is the C drive, then yes, you could say that the OneDrive local is as fast as the C drive.

Not sure what this question even is supposed to mean. OneDrive is a virtual cloud drive that still uses a specific folder on your local hardware drives as a cache and of course depending on the performance plus the added overhead by syncing with a web server with all the potential caveats it simply can never be faster than your actual physical drives. You have some serious misunderstanding here.

Mylenium