It's not so much the speeds and stability - can't be much worse that NTL, surely

It's the hassle of switching versus the savings. Just weighing them up and seeing where the scales settle. Just can't decide.
Getting a filtered face plate does seem to make an incredible difference to the speed, so that would be factored into the cost - plus the CAT5 extension. Cost me about £40 to do a similar thing for my mum - worth it though for the speed increase.