That's an interesting link you posted! I never even knew that speed comparison tables like that were compiled.
Anyway, I've been with Pipex since February, and it's only failed once, and that was for a few hours one Sunday. I notice, though, that Tesco are now offering a 512K service with unlimited downloads, free connection and free modem, for £19.97 a month. I don't know how reliable or speedy their service is, but it might be worth checking out.