I have always wondered how using Internal IPs would effect the data transfer rate between two instances on AWS compared with when using EIP or domain. To answer myself i conducted some tests today and results are shown below:
14.46MB/s 15.54MB/s 14.45MB/s 14.46MB/s 14.46MB/s
15.54MB/s 14.46MB/s 14.46MB/s 14.46MB/s 14.46MB/s
13.53MB/s 14.46MB/s 14.46MB/s 13.53MB/s 14.46MB/s
As you see the difference is of a very small magnitude. There is one point i would like to mention here though, if there is a congestion in network, it affects all three in same way. Later during peak hours, tests showed speeds to be around 3.4MB/s and even 300KB/s but that was independent of the destination type (whether it was domain, or Elastic IP or Internal IP) used.