I'm 100% sure that even with a sync of 20000Kbps you need to give overhead and the actual throughput ends up at 18.7Mbps or slightly lower
Doing the math, 18.7Mbps = 2.34MB/s. That means every hour you could upload 8.42GB
8.42GB / 2 = 4.21GB every 30 minutes.
That's not taking into account the fact that the upload speed could drop slightly or fluctuate through the entirety of the upload, depending on where you're uploading too and what kind of load their servers are experiencing.
I'd agree with itsme and say 3.86GB in 30 minutes sounds about right.
