I,m on 20mb virgin media (formerly NTL)
The best way of testing your speed is downloading a good .torrent (usually from a private site) file or from a nzb file (newsgroup)
Not one of the tests i have done from any of the links given in this thread are accurate.
some giving me 511 kb,s and some 14,320 kb,s etc
for example
I have just downloaded a 705mb . torrent (lots of seeders 4000+) file in less than 8 mins and was nearing my max 2024 kb,s
Cable all the way
