I've found that landing pages are less of a design issue and more of a messaging issue, although having something attractive is certainly nice to have. If you're largely taking existing headlines and making them look nicer, you're missing greater opportunities for improvement.

I also don't think saying you get 10% - 17% conversion rates resonates at all. A lot depends on what you're optimizing for. I have landing pages that can routinely convert 70-75%, but that's a first step optimization for click-thru, not sale. I think it's best not to pigeon-hole yourself into a range and instead just say "I've increased conversions by x%".