Since the "peak" hardware is a dual E5-2660v2 thats 32 threads, so a c3.8xlarge would be a much more comparable instance.
I've noticed a weird trend where amazon created various slices of instance types a long time ago, and people have mentally gotten used to using larger ones far slower than moores law adds cores. So people will refer to something with 2 cores as "middle-of-the-road" and 32 as "extremely high-end" when in my brain thats "a cell phone" and "a 2 year old server".