It's not throttling. Even if it were SSL would be an exercise is futility.
'Oh look we have customers opening 10 SSL connections to europe.news.astraweb.com - well that's ok we'll throttle NNTP but we'll leave those 50Mbps SSL connections alone, clearly not NNTP riding over SSL'
EDIT: Just to show how fast and easy this would be, Giganews have this IP range:
Giganews, Inc. GIGAN-CIDR1 (NET-216-196-96-0-2)
216.196.96.0 - 216.196.111.255
So just shape everything there apart from the Giganews speedtest (Just allow the first say 10MB to go full speed and customer will get a realistic speed test)
Astraweb nearly as easy.
netnum: 91.208.207.0 - 91.208.207.255
netname: Searchtech
descr: Searchtech Limited
inetnum: 193.202.122.0 - 193.202.122.255
netname: searchtec-ams
descr: Searchtec
207.246.207.0/24
215.151.153.0/24