njs7227, about this:
I thought a CDN was supposed to improve site's performance but my findings were not supporting that.
It actually does. It makes pages load faster in most cases. Don't rely only on scores. Every file hosted on CDN adds a redirect (request is actually made to a local origin and W3TC is redirecting it to CDN version). Google Page Speed, YSlow and other tools decrease your score because of that with a simple recommendation - 'minimize redirects'. Check your site with http://tools.pingdom.com and review the results in detail.
Serving static files from CDN means that a user can send more simultaneous requests and download more files/assets at once. At the same time, serving large files from CDN decreases your server load, and it definitely improves overall performance, especially for high traffic websites. This makes a huge difference if you have short ping to CDN servers. I live in Ukraine, the closest and fastest S3 location is Ireland with 150-200ms ping. US locations are even slower. So, for any local ukrainian or russian visitor serving files from a local ukrainian server with 15-25ms ping will be much faster.
