HTTPS also increases the page load time, and there's plenty research that shows the relationship between latency and CTRs.

I'd like to add a shameless plug by noting that I'm working on a project that renders performance and security much of a false dichotomy within native iOS applications. We hope to incentivize the capitalists in the room to secure their applications by coincidence of making them faster. Caffeine: http://www.caffei.net/