I had the VM 50mb package for a while, its full of crap. throughout the entire time i never once received the 50mb it stated i would get. it varied from 9-28mb. midnight etc i would get 20+, during day i would get around 10mb. fibre optic BS if you ask me.
its a lottery ticket imho, if you happen to be in the right area then bingo you'll get full speed.
i'm with O2 now and i get a solid 20mb line constantly, its a shame the modem they give is not as good as the line connection.