I decided to try Cloudflare this holiday weekend on a bunch of my sites -- all of which are also running W3 Total Cache with Cloufront CDN.
I had a few questions along the way and submitted tickets in the CF dashboard. Within minutes (on a holiday weekend!) I received answers that got me on my way. It was the best support I have EVER seen.
I have been testing my sites and I'm seeing very clear speed improvements with CF added to the W3TC/Cloudfront setup. I considered my sites highly optimized before trying CF -- and now they are simply screaming. I'd say CF reduced load time of every site by about 10%. I'll take it. The response time of my site with the highest traffic went from about 490ms to 440ms -- and the total load time was reduced by more -- I'd say about 25% -- from just under 2 seconds to around 1.5 seconds.
These results are with the "Pro" account level which enables the "Rocket Loader" feature. Well worth the money.
If you have any questions - ask me. If you have a busy site, lots of plugins and significant traffic, W3TC/Cloudfront/Cloudflare is the killer combination.