I have a server at home running Windows Server 2012 Standard (RTM). The server is accessible via VPN (SSTP) over the internet. This works pretty well.
But when I access one of the shared folders from another computer (Windows 8 Enterprise RTM) using the VPN, the connection is sort of slow. "Sort of" because it is not really slow but kind of choppy (hard to describe as I'm no native speaker). I found this out while listening to an audio file from my server. My internet connection at home has 1 Mbps upstream - which should be enough for streaming an MP3 with 192 kbps to another machine. Although, playing the file over the internet doesn't really work. Every 10-30 seconds, the music stops and continues after a few seconds, like a buffer underrun. I then tried to copy the file to the local computer first and found out that even the copying is choppy. The progress bar stops for about 10 seconds, advances 1 MB, then stops again and so on. The whole copy dialog is pretty unresponsive the whole time. Cancelling a copy job took 15 seconds.
Then I wanted to find out whether it is really a problem with the shares. So I downloaded a file from my server again - but this time using HTTP and IIS (and still using the VPN). This download worked as expected: a smooth download with a constant transfer rate of ~1 Mbps.
So what is the problem with those shares? Local shares work perfectly on both machines. So do downloads via HTTP in the VPN. Just the shares via VPN are having problems.