Thanks for the inputs @aaronmefford, I'll see if I can quickly run through those tests.
Couple of questions:
a, Can you provide more details on your bulk sizes? size, frequency, synchronous/asynchronous, etc. I'm facing some challenges on the response times from bulk indexing.
b, m3.2xlarge is 8 core whereas m3.xlarge has 4. Do you think the number of cores made the difference or was it convincing that the extra heap space is the truly differentiating factor?
c, Were you able to figure out what goes into the 2GB of space? It would appear that instance types like c3.large (4G memory) instances won't even seem like a good choice for elasticsearch.