There are a ton of variables that affect website performance --- location, connection speed, browser used, etc. There is simply no possible way to get an accurate measurement of how a CDN will impact the performance of your site without using RUM (JavaScript instrumentation of the page to record the actual experience for every visitor). Every website has a unique audience with unique characteristics. We offer a free RUM tool at Torbit for anyone interested in getting an accurate measurement of how Cloudflare (or any CDN) is performing.
Check out how Wayfair used Torbit to measure how much of a difference Akamai was making to their site: http://torbit.com/blog/2012/07/23/wayfair-uses-real-user-mea...
If you're interested, I'd love to help you do a similar test for your site.