All things being equal (other than length), and tip stiffness identical, the extra length of the pole should give added distance to your cast. Even on the surf at Assateague, I use 10' - 12' poles, but in surf fishing, longer poles also help keep the lines out of the wave breaks, thus not dragging the rig in with the wave power. Depending on your type of fishing, pier, beach, surf ect., match the length with what you are doing. Me as I said am primarily a rookie surf-fisher thus my longer rods, but, as I do more pier fishing (Tank), I think I'll go and get maybe a 7' - 9' set up with short butts.
Just me two cents worth.