Actually the SPEED TESTS performed with the VPN are not at all accurate.....In short, the results may surprise you, but the speeds are always with in the Limits of your ISP....I, myself had this situation.My download speed is 50 Mbps and after connecting to my VPN, my speed was 72 Mbps. But I tried to download YouTube videos, but my old speeds were Predominant...Most of the times my Internet was slower than 50 Mbps. Generally VPN throttles your speed rather than Boosting it up since data has to be transmitted to VPN servers first, then encrypted and then sent back to you...All this process results in a lot of time delay and hence the Capping of Speeds....But Speed Test server connects to the VPN server and test it's speed rather than testing your speed....Hence the illusion of Speed Rise.....
