Only a Rails developer would think 6k requests per minute with 40ms latency is reasonable with all that hardware. If you rewrote it you probably only need 1 server but you will probably make an argument about how developer time is more valuable :)
I'm talking about a real application here. With 100s of database and API calls on each web page load. I could make the whole thing in Golang or Scala and that would be at least one order of magnitude faster. But then I would have to throw away all the business knowledge that was added to the Rails app.
For instance, the slowest API call on the 40 ms is one that hits an ElasticSearch cluster with over 1 billion documents and is made on a Scala backend using Apache Thrift. There's a lot of caching but still, long tail and customization will kill caching at the top level.
What type of business that someone would basically run out of an office closet like this would need to service more than 6k requests per minute?
Swinging the conversation beyond the dosages of either side doesn't produce interesting insight