then possibly the answer isn't a 'benchmark ahead of time" approach, but is instead a "run it for a little while and then ask it for recommendations of things to try"
I am the type of person who tends to appriciate manual knobs to tune things, however when the normal answer to any performance question is "well, you must have things tuned wrong" without there being any way for a newby to know how to tune it, there is a problem.
The fact that MySQL has historically done better for simple queries with the default configuration leads people to be scared of Postgres.
In many ways, this is the same way the Microsoft made it's way into the corporate datacenter. They pitched it as "no expertise needed to run it, just install and go", and for small, simple setups they were close enough to right for people to believe it. The fact that running a large setup on Microsoft products frequently requires more resources, and more experise than running the same userbase on a *nix solution is missed by many people because they got started cheaply and so they assume that the ramp-up is going to be equally hard for competing products.