Google’s mod_pagespeed and Cloudflare have no known conflicts at this time. Cloudflare’s CDN and optimization services will generally be faster because Cloudflare is a CDN (content delivery network) as well. So running mod_pagespeed will likely be somewhat redundant. Many of the features offered by mod_pagespeed are also already available in Cloudflare’s feature set. With nothing to install on your server at all.