Please note that I use HTTrack to mirror internal websites on a corporate,
internal web, with NO connection to the Internet.  Speed is no problem on our
internal web - 100Mb/sec is standard, vice 1 Mb or so on dsl.  Downgrading
HTTrack to force low-speed connections would limit my ability to use this
tool.

Regarding other robots:  I used to use Teleport (not as good, also expensive)
which ran 10 threads at a time....  Maybe your company should also sue the
makers of Teleport, but they probably have lots of money and lots of lawyers; 
it might be cheaper to get a server that can handle today's loads, where large
numbers of simultaneous, high-speed connections to a single machine are not
unusual.