The problem with NH is related to the number of threads you need to use, not total bandwidth.
It is NTL specific, but I dont see why NTL would limit the speed on any particular thread, when you can just up the number of threads to max your connection anyway.
i.e. If I download using just the 8 'allowed' threads - slow performance 400k/s. up that to 15 or more connections and I'm back to 1.17mb/s.
Now I've used other newsgroup providers and do not have the same problem with them (as I've told NH support) so either NTL are specifically restricting connections to NH only, or its a NH problem. (or possibly something with the route NTL users take to NH).
Personally I dont think its traffic shaping or anything deliberate NTL have done. But there is a problem somewhere.