Site Speed Optimization x 10 sites - repost

Hi, I had 10 wordpress sites and I would like to optimise the speed of the sites. Most of my site are doing pretty good in B or loading time of 3 seconds. Requirement as the followings: a. I will check all sites in [login to view URL] Most of my site is in B. I would like both site speed and Y Slow to achieve A grade. b. I will check my site in [login to view URL] If possible, I would like my site to be loading under 1 second and faster than 80% of the rest of the site All of the site had been optimised for database, use CDN for photo (photon from Jetpack Wordpress) and WP Minify for javascripts. I don't want to install any plugin to my site. I had already got too many if I install further that will slow down my site. I need your advise and I will appoint someone with previous experience for this type of job.