My highest traffic site is fundmanagersoftware.com, and that was transitioned last, on Sep 4, 2014. The yellow "Change Date" point graphically shows the date where the site was changed from HTTP to HTTPS. I'm plotting both the "HTTP Impressions", as well as the "HTTPS Impressions", plus the sum of these two as "Combined Impressions". You can see shortly after the change date, the HTTP impressions drop off quickly, while the HTTPS impressions take over. Their combined sum stays relatively consistent with impressions before the HTTPS transition. The "Combined Clicks" are also shown, and you can see these also stay relatively consistent with pre-transition values.
My next highest traffic site is beiley.com. This site was transitioned on Aug 31, 2014. Again you can see how quickly the impressions transition from HTTP to HTTPS after the change date. For some unknown reason there happened to be a spike in impressions shortly after the transition, but the clicks remained relatively consistent with pre-transition values.
automsw.com has less traffic, and was transitioned on Aug 21, 2014. Looking at the combined impressions and combined clicks the data looks relatively consistent with pre-transition values. It does look like there might have been a slight drop in impressions after the conversion, but it is hard to say, as there started to be some lower impression counts right before the transition as well.
My lowest traffic site is email-announcer.com, and it was also transitioned to HTTPS on August 21, 2014. This site's results also indicate impressions/clicks remained relatively constant through and after the transition.