Q:

How to find the "most efficient" users on StackOverflow

Is there a way to find out who are the most efficient users on StackOverflow (given a certain reputation threshold)?
What I mean by an efficient user is one who has the least amount of posts (either asking or answering) and gained more reputation.
Example
Let's look at two hypothetical users (userA and userB)
userA
Reputation: 5000
Answers: 250
Questions: 10

userB
Reputation: 5000
Answers: 350
Questions: 100

In this example, I define userA as the more efficient user since userA has been able to reach the same reputation (5000) with less posts.
Of course, there are so many qualitative variables that aren't factoring into my definition (e.g. quality of posts, time of day spent on the site, etc.); however, I'm solely concerned with the quantitative data.
I suppose a simple calculation, for an "efficiency index", could just be to take the sum of the users posts (250 + 10 = 260 for userA and 350 + 100 = 450 for userB) and divide the reputation by sum.
Example:
userA = 5000 / 260 = 19.23 (higer efficiency index)
userB = 5000 / 450 = 11.11

Of course, this is just as simple case. Ideally, It would be nice to ask questions like:

Who is the most efficient user under 2,000.
Who is the most efficient user between 5,000 and 10,000.
Who is the most efficient user overall. 

I understand this could be quite tricky and obviously you would want to consider filtering out users that have an artificially high efficiency index.
I appreciate the feedback that the community has to offer. Thanks.

A:

I have some results with this query (feel free to fork it and experiment yourself, e.g. by setting the reputation limits):
SELECT u.displayname, u.reputation, COUNT(*) AS numberOfPosts,
  u.reputation / COUNT(*) AS score
  FROM users AS u
  INNER JOIN posts AS p
    ON p.owneruserid = u.id
  GROUP BY u.displayname, u.reputation
  HAVING COUNT(*) >= 10
  ORDER BY score DESC

I took a threshold of at least 10 posts, here are the top results:

