[jwr]

> the "performance" you were testing was disk IO throughput

In part, yes, but not entirely. I was very clear that my load isn't embarrassingly parallel, so it is not expected to scale linearly with the number of processors.

> You seem to be implying that AWS/EC2 does CPU over-provisioning on all instance types; this is incorrect, only T-family instance types use CPU over-provisioning.

If you think you are getting a Xeon core when paying for a "vCPU" at AWS, I have a bridge to sell you.