Due to a mistake I reserved an aws RDS instance with 1 CPU and 3.75 RAM - not ideal, but I did this for a year in advance. Crap! Naturally, Drupal the resource hog as it can be is dancing on the 90%-100% CPU usage line here. I was planning on at least 7.5 RAM and TWO CPU's I'm fucked!
I have Varnish 4 installed and working
I have Drupal default cache on (when I turn on Authcache, default fails and Varnish 4 fails)
90% of traffic is anonymous so caching as much as possible is obviously ideal.
The Drupal 7 install that I have is Pressflow optimized.