Most of the 1200 use it at the same time. My webservers are behind the load balancer, but newrelic - the performance monitoring tool has lately started showing

Most of the 1200 use it at the same time. My webservers are behind the load balancer, but newrelic - the performance monitoring tool has lately started showing app server times taking as long as 1200ms. Rather than add more servers I wanted to hear from others if 2 instances for 1200 users is in the ballpark, or is my application poorly designed.