The main objective of a good Internet client connection to a media-streaming server is of course download speed, but when connecting through a VPN if your home connection's upload speed is not good it could be choking your download speed, especially if your Internet connection is shared by several users and/or devices.
Here's why. Most proprietary media-streaming client-server protocols don't require a lot of Level 2 Internet-layer TCP/IP communication between your machine and theirs, so a typical Home High Speed Internet plan will be satisfactory. In willise's high-end Fibre example we can see that he has a huge pipeline up and down between the client and server. Add to that the fact that any communication between the client and server is up in the higher Transport and Application layers where it is optimized to greatly reduce network load by a number of means and you have a blazing fast connection but at extra $$$ to the consumer.
when the connection to the server is wrapped through a VPN service you can see the cost in Level 2 Internet-layer TCP/IP overhead as the client now has to respond with an "ACK" packet before the server can send the next payload, even though the original higher level protocols are working perfectly in their optimized state. This is why upload
speed is so important for good VPN connections rather than just download speed. ACK packets are tiny, but when you get enough of them queued-up on your home network while other users and devices on your Internet connection are also using it, you get traffic jams that cause slowing. Sometimes even with a high download speed Internet plan the upload speed is just not enough to handle it all, and your media-streaming begins to suffer slower downloads (in the worst case causing jerking and skips in your favourite program).
If you find that using a VPN service is unacceptably slow, you might need to get a better Internet connection plan for your home with higher upload speeds. Take at least 3 different Web-based connection speed tests to their nearest test servers to get a realistic idea of your Internet upload
performance with and without VPN. It is best to run these tests while your home Internet connection is under its heaviest typical load:
Write down the average upload speed given by each test with and without
VPN. Generally the results you get will be quite similar from each test, but if one gives very significantly lower results than the others there may have been a unique problem with it so just discard that one and carry on. With this info contact your ISP and ask how much improvement in upload performance can be purchased. ISPs focus their consumer plans onl download performance, so generally a higher plan will boost both. Shop around too.
Looking at willise's numbers he is absolutely fine with or without the VPN connection due to that splendid ~5Mbps upload capability on both.
Hint to networking geeks: apply traffic-shaping that bumps up ACK priority, but as always: test, test, test!