So my question is what if I have a 6'6" Medium Fast rod and a 7'1 Medium Fast rod (same type and same manufacturer), other than gaining some distance for casting, what is difference in performance? 

A longer rod lets you move more line when setting the hook.  Basically giving a smidge more authority to the hook set.  World changing?  Nope.  The difference in casting distance is a bit over rated as well if you ask me.

 

I use 7 ft. to 7'4" rods only out of slight personal preference.  That's it.

 

Others may have different take on it.

ok that makes sense..thanks

I think the length definitely adds casting distance but is only negligible on hooksets.  

1 hour ago, jbrew73 said:

I think the length definitely adds casting distance but is only negligible on hooksets.  

I'd have to agree with this.  My 7' or longer rods definitely cast further than my 6'6" rods.  At least in my hands.  As far as hooksets are concerned, I try not to have much slack line when I go to set a hook.  I prefer to remove all slack if at all possible.

Shorter rods more accurate, longer rods more distance. In the end personal preference.