My coworker has the same VPN service I do and he claims that he sees no degradation in his speeds when he enables it. I would be willing to believe that I am simply hitting the maximum speed for the VPN link except for the fact that with Bell, I was generally seeing speeds around 2.7MB down with the VPN enabled, with Rogers the fastest I've seen so far is around 1.5MB connecting to the same endpoints. I've spoken to the VPN tech support and they want me to try all protocols and ports that their client can use and if that doesn't work, they want screenshots of the speed differences. According to them, I should see no speed hit at all.
Also interesting to me was that if I leave the secure NNTP protocol to the default of 583, the speeds were again degraded, but when I changed it to 443, they went through the roof. No matter what Rogers says, it looks to me like they are still throttling certain protocols.
I was with Giganews for years, but ultimately, thier prices drove me to their competition. I had no complaints about thier service while I was with them though.