If I'm understanding it right over hang is the amount of running line that is out side the rod tip top ring.
Yes, more or less. It seemes that the term "overhang" is used more by people using shooting heads and very skinny running line (like monofilament). Generally speaking, most people using regular WF lines refer to the amount of line they are "carrying" or "aerializing" just prior to the final shoot. That includes head and running line.
Is there a right amount of running line that should be out side the rod end say like 2ft,4ft,6ft, and so on in order to help shoot line more effectively?
No. In addition to differences in the line and rod as Randy said, the length will vary with the caster's style and wind conditions.
When I hear conversations (or rather read them) among competitive distance casters talking about how much line they are carrying they always mention the specific line. Sometimes the rod, but most of them know what rods the others cast, and the rod makes less difference at that level than the line. Here is a link to one such conversation where the original poster has the identical question as you.
You may note that only the original poster mentions the word "overhang". For that term to mean anything, the person you are asking the question of would have to know the head length of whatever line you are asking about. And then he'd have to subtract that length from however much line he carries.
I can probably make that more confusing for you if you'd like.