For what it is worth, I found the Rackspace Windows Cloudservers (Beta - various sizes) to have amazingly fast IO (500+mbs). They were 4-7x as fast as the EC2 instances I tried. (70-120mbs)<p>I was just using ATTO. Is this a valid test? It was at least twice as fast as my RAID10 dedicated server (240+mbs).
EC2's IO performance depends on type of instance storage (ephemeral or EBS) used and instance size. The m2.* instance sizes with EBS actually outperformed rackspace in our tests, whereas m1.small performed about 2/3 slower than Rackspace.