You can open up the Resource Monitor in Windows and filter by eso.exe to get the current Bytes/second. On startup it's quite high, ~1100 - 1900. After a minute or so it declines to ~500. So, given that 500 B/s, 60 seconds in a minute, 60 minutes in an hour roughly equates to ~1.8M and can get as high as ~7.2M per hour. A relatively slow network should still be able to handle that.