Recently I was involved in a project, which involved converting all links from http to https, basically making the site SSL enabled. After we did the changes we needed to measure the performance of the pages. You can test this using a combination of techniques described here :
a. Using chrome developer tools, you can actually see how much longer each script or image is taking to load
Detailed blog post over here: https://developer.chrome.com/devtools/docs/network#resource-network-timing/
b. Using the performance timing interface mentioned here: http://www.w3.org/TR/navigation-timing/ you can fine tune your measurements.