I have a similar dilemma, or 'had' as I have taken the plunge.. .scrapped Virgin Media 2Mb @ £17x/month + will soon order O2 broadband at £12 for up to 10Mb, which will reduce to £7.34 or thereabouts when I migrate my mobile phone to them in July.
Total savings. about £200 x year (or about 113 pints of beer in old money)
For that I'm willing to forgo reliability as I have found something better to do apart from surfing the Net
(*)
(*) no, not that...learning to play the guitar 