The guys at DigitalOcean have written a great article with the choices you have when designing your webapp insfrastructure needs:
Digital Ocean is now offering the possibility to deploy Ruby on Rails with Ubuntu 12.10.
I will be able to give you feedback about the experience once I try it!
Thanks to this article http://www.chimerasaurus.com/2013/01/nginx-requestssecond-raspberry-pi-vs-amazon-ec2/ I have learnt about the existence of Phoronix Test Suite which I would like to try in my servers to find out whether the performance is better with nginx or apache.
And another option to run performance tests is Blitz.io