Ask HN: How can I A/B test my Positioning Statement?

I ran a campaign on Google Adwords to do this, but I feel that the results were a little inconclusive - 1. because I had to try and squeeze my copy to fit the character limit (so in some cases I had to test a variation), and 2. because there are too many other targeting variables so it's not clear whether you are reaching the same audience consistently.

Are there any self-service, easy to use market research tools out there that will allow me to test 5-10 positioning statements (and/or landing page design) and see what works best? It would also be useful to get qualitative feedback, not just quantitative.

Any other ideas on how I could I go about getting conclusive evidence of what works and what doesn't?