> httrack usually loads only at about 25 KB/sec., even
> if I set the download speed to 9999 KB/sec.
> This limit seams to be present independend how fast

It is. It is a security setting to prevent overloading the server crashing it
or getting your IP address banned because of a DOS attack.

You must override the security switch before it will look at values above 25.

Have you read the abuse faq? <http://www.httrack.com/html/abuse.html#USERS>