Any transparent proxy? - Compare results from whatismyip.com and ipchicken.com - same result suggests no transparent proxy, different result suggests that there is a proxy.
blocked smtp ports - outgoing smtp tcp/25 should be blocked, but other smtp ports should not. telnet smtp.gmail.com 465 (you should get a blank screen and not an error message) telnet smtp.gmail.com 587 (you should get a "220 mx.google.com" banner) telnet smtp.gmail.com 25 (expect this to be blocked, with an error message)
- multiple-connection download. try the above using your download manager
International download speed - single connection. Can you download your 4gb file without using download manager? is this from a premium ddl service like megaupload, hotfile, etc?
- multiple connection download. if your download manager could download a 4gb file in 6-7 minutes, that is approximately 4000 MB / 420 second ~ 9.5 MB/s. That is very very good in my books.