Is there a relationship between EI (Emotional Intelligence) & Leadership effectiveness ?

yes, especially when relating with clients and employees. it makes you not to act according to how your emotions want you to act.

I answered a very similar question to this the other day:-

 

http://www.bayt.com/en/specialties/q/218428/is-emotional-intelligence-eq-a-pre-requisite-for-all-leadership-positions-and-to-what-extent-can-one-exercise-this-skill-within-any-work-setting/?utm_source=specialties_transactional&utm_medium=email&utm_content=10&utm_campaign=specialties_transactional_emails_en#answer_750678