Originally Posted by
moondog
Interestingly, I downloaded some TV shows yesterday. With the VPN off, I was getting something atrocious like 15k down. But, after turning it on (Chicago server), that shot up to 100k in a matter of minutes. I suspect that my ISP is probably throttling P2P bandwidth. Strangely, skype seems to work better with it on as well. I'm not sure why.
This could well be the case. Many of the ISPs here throttle the bandwidth depending on the internet port that the connection goes through on (for good reason given the amount of downloading that goes on ....).
When you connect through VPN the ISP only sees the (encrypted) internet traffic going to the VPN port/address. This may be fixed or variable depending on your VPN provider, and so is another potential source of day-to-day variation in downloading speed.