330,000 page views per minute is 5500 page views per second. With 6 load-balancer servers that comes out to ~920 per server. This seems to be below of what HAProxy can handle. It seems like you severely over-provisioned that tier. Speaking of load-balancers, it would be great if you guys updated your article from 2010 http://blog.rightscale.com/cloud-management-best-practices/benchmarking-load-balancers-cloud with the currently viable choices.