Fair question. We had some reservations about using EC2 for the reasons you mention. But we wanted to avoid any perceptions that we'd somehow cooked the books

Fair question. We had some reservations about using EC2 for the reasons you mention. But we wanted to avoid any perceptions that we'd somehow cooked the books, so decided to run the tests on "neutral" gear. If you look at the report details, you'll see some of the lumpiness your question suggests, particularly related to the network. The Node instances were beginning to starve when database server CPU utilization was still pretty low. We would certainly have gotten better numbers if we ran these benchmarks on bare metal or a closely-tended cloud infrastructure. But we're a pretty low-BS group, so we'll stand behind what EC2 gave us.