The results, post migration, shown below. This is one of my Shopify Apps going from a monolithic Rackspace instance to a 2 instance load balanced setup on AWS.
Performance is consistently good now at just under 50ms response time.
I split out the background processing stuff and Redis onto their own instances as well so not sure exactly what was the biggest bang for buck.
I'd say the overall experience with OpsWorks is very good once you get over the learning curve and setup pain.