Use of "skill" and "competence/competency" in specific scenario

Question

To me, skills are something related to mechanical performance. Someone is very skilled at playing football, for instance.

Competence/competency on the other hand is more related to knowledge. Something that is not mechanical.

What is the correct use in this very specific scenario?

Suppose you have the Stackoverflow site (asking questions and answering them). Which word would we use if we wanted to describe individuals with the highest reputation in specific tag? Like C# (as in C# language). Do these users have competence/competency or skills?

We could say He's very skilled in C# language, but in a differently formulated sentence, it would be better to say His competencies are (in) C# language, software algorithms and ... Or would it be better if we used skills? My gut feeling says the former is better. But is it really? And why?

And while we're talking about it, why not also define the difference between competence and competency?

Edit

I would also like to add the third term that could be used in this specific Stackoverflow scenario. Proficiencies. I suppose this term could be used only for those users with gold/silver badged tags (similar to what users have here if you don't know Stackoverflow). Or describing users with top reputation in general without explicitly listing their top ranking tags.

In such scenario we could also talk about experts with expertise (is there even plural of this word?).

Answer 1

While "competencies" and "skills" are synonyms at a surface level, "competencies" is (in my experience) generally used in a narrower business context. Since 1990 the term "core competencies" has come into vogue for business discussions, which may also have some impact on the use of "competency" as a way to infer not merely the ability to do something, but a certain degree of fluency, effectiveness, and competitive advantage. While "is skilled at" and "has competencies in" are really quite similar, I would argue that the use of "core competencies" as a business concept might impact associations with the word "competencies" in business contexts.

I would reject your assertion that "skills" need to be mechanical; however, there is idiomatic difference between "being skilled" and "having a skill" as the former implies some level of expertise and the latter merely implies that someone has an ability.

On Core Competencies: http://www.investopedia.com/terms/c/core_competencies.asp