Yes, the differences between graphs were fairly substantial. You can get a sense of the EBS vs. ephemeral difference by looking at the "Throughput by Threadcount" graphs (about 1/3 of the way through the post). Briefly, EBS has much higher throughput for random writes; ephemeral (instance storage) is faster for reads and bulk writes.
One question: on the throughput graphs, I understand why you normalized them per graph, but were there any differences between graphs (particularly in terms of EBS vs. ephemeral) that would be sufficient to drown out the variability within the throughput graphs?