In response to question #1. I've conducted some similar benchmarking across all instance sizes and using both ephemeral and EBS with and without Raid. EBS is notably faster on larger instances. We observed roughly 2.5-3X better IO with EBS backed m2 instances compared to c1.medium. Using ephemeral Raid 0 on the cc1.4xlarge was about 6x faster.

http://blog.cloudharmony.com/2010/06/disk-io-benchmarking-in... http://blog.cloudharmony.com/2011/04/unofficial-ec2-outage-p...