Measure impact of using prerender via Webpagetest

gistfile1.txt

// Because we aren't technically making the page render any faster, the page we navigate too isn't reporting 
// a decrease in render/speedindex/etc, which makes sense. But how would you measure the affects of prerender?

// If I use this same injection strategy locally, give the prerender target page some lead time (a couple seconds or so)
// then the effect is a nearly instant perceived page load. But it's unclear to me how I can measure that. Halp.

// * These don't work *

// inject the prerender tag, give the target page a 1000ms lead time
// result: http://www.webpagetest.org/result/160316_13_cc82666824bc7c89a88336b60eaed1fa/
logData    0
navigate    http://www.curbed.com/
exec window.preTag = document.createElement('link');
exec window.preTag.rel = "prerender";
exec window.preTag.href = "http://www.curbed.com/2016/3/15/11234274/japan-earthquake-recovery-home-for-all";
exec document.head.appendChild(preTag);
waitForJSDone  setTimeout(function(){ window.webpagetest.done() }, 1000);

logData    1
navigate    http://www.curbed.com/2016/3/15/11234274/japan-earthquake-recovery-home-for-all



// inject the prerender tag, give the target page a 4000ms lead time
// result: http://www.webpagetest.org/result/160316_6N_bb6e961571757acaa650e1cf976480c7/
logData    0
navigate    http://www.curbed.com/
exec window.preTag = document.createElement('link');
exec window.preTag.rel = "prerender";
exec window.preTag.href = "http://www.curbed.com/2016/3/15/11234274/japan-earthquake-recovery-home-for-all";
exec document.head.appendChild(preTag);
waitForJSDone  setTimeout(function(){ window.webpagetest.done() }, 4000);

logData    1
navigate    http://www.curbed.com/2016/3/15/11234274/japan-earthquake-recovery-home-for-all