My VPN appears to be making my cable internet connection 5X faster?
Solution 1:
Either your ISP is throttling your connection or there is a routing bottleneck somewhere between your ISP and where you are downloading from that isn't present between you, your VPN, and where you are downloading from.
Roughly the way your VPN works is that it encrypts the traffic and sends it over a different protocol (say IPSec) between you and your VPN. So if your ISP is trying to throttle certain things rather than your entire connection (say by scanning HTTP packets) then their throttling tools wouldn't be able to see the traffic in order to throttle it, hence bypassing their throttling.
I had the same issue with Verizon FiOS and saw about a 10x speed increase when using a VPN (same one, btw). After some digging I narrowed it down to downloads from Amazon S3 east. Amazon S3 east is the default datacenter when serving files from Amazon S3, and a lot of sites/applications serve content from Amazon S3 east (at least a lot that I happened to use). Whether Verizon is throttling or it is just routing I don't know.
Solution 2:
The real question lies to if you get these speeds while downloading actual files. Try testing your internet using http://testmy.net/ It'll simulate an actual download of a file instead of pings to and from a server. I've found it a lot more reliable to the actual speed of my internet vs Speedtest/Speakeasy/Xfinity (which are all practically the same).
Solution 3:
Well, I have a very different answer to your question and by the way what you have got for the speed test is correct and true! In some ISPs, they are monitoring and auditing your packets and using sometimes something called content filtering which can filter, or block some prohibited websites in your country/isp. By using vpn connection you are bypassing this filter, or even site blocker by your unmonitored anynumous data which can make your connection faster again.