Originally I wrote: "I'm getting from 20+ to 27 seconds delay..." It was really a terrible pain - a single forum page was refreshing for 20+ seconds instead of 2-3 seconds.

The issue is finally resolved. I nailed the reason and informed my provider. I guessed it could be interesting for all of you to know about the real reason. Here is the link to get some info:
http://www.myfoottalk.com/default.aspx?g=posts&m=155#post155 

It's actually googlable if you try one of the IP addresses with the port 12200 scanning your machines and routers.

These [censored] people are slowing the whole Internet down. The preferences are SQL Servers, sometimes IIS and other services remaining open. So people be alert! I analyzed the IP addresses these attackers are coming from. There is a good way to block all these ranges on your firewalls to keep your networks safe.

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