Some great posts:

40 Million hits a day on WordPress using a $10 VPS

and the original: https://ewan.im/900/10-million-hits-a-day-with-wordpress-using-a-15-server

See also https://stackoverflow.com/questions/28519265/when-should-i-use-a-t2-medium-vs-a-m3-medium-instance-type-within-aws