If that's the fastest that they say is available for your area (and considering your experience + the fact you use VoIP), then a move away from CL is probably best. It sounds like they may not serve many in your geography and as such you're probably forced to be working on pretty bad infrastructure. For the $$, I think Comcast will probably be far superior, even if you're not on their high-end speeds.
Century Link should be ashamed for selling to you at a rate that isn't steeply discounted, and then not even providing what they're advertising. But then again if the customer base doesn't demand... Good luck either way.