I have done lot of experimenting with different FREE CDN's (CloudFlare, Incapsula, Google PageSpeed Service), and they all work good, but the performance level are only to be seen with CloudFlare & Google Page Speed (Page Speed is only at google's consent to provide you).
but be very careful when activating CloudFlare on Moodle, start with all basic settings, NO cache of JS,HTML,CSS, Security settings: Medium, and performance: CDN Only, TTL: 4hours, Cache-Level: Basic
rest keep OFF, as RocketLoader tends to play-up with few plug-ins of moodle.
after 2 days, start turning ON things, best bit would be selecting the CDN +Basic Optimizations in performance tab, and keep TTL to 4 hours (as selecting CDN + Basic will increase it to a day).
keep security settings as medium in any case, else it will be blocking clients for no reason.
also, dont turn on KEEP ALWAYS ONLINE (unless you have really bad uptime with server), as I have seen in cases, keeping this ON, cloudFlare do advertise them time to time by showing page saying, "server has no response, but this site is hosted on cloudflare always online technology - click here to learn more".
rest, depending on your content, you CAN enable RocketLoader too (didnt worked well with me, as I am using Tabs Filter so loading use to get stuck), but it really gives a kick to your site's performance.