This seems pretty wild to me. Are you saying that I can submit instructions to the CPU and they will not be interleaved and the registers will not be swapped-out with instructions from other EC2 virtual server applications running on the same physical machine?
Only the t instances and other VM types that have burst billing are overbooked in the sense that you are describing.
Yes — you can validate this by benchmarking things like l1 cache
Welcome to the wonderful world of multi-core CPUs...