If you already have the 9 6" then use it. It really depends on what type of fishing you are going to be doing. My ideal rod for fresh and salt is a 10 6" single handed rod. I don't really notice that big of a difference in a 9 6" over a 9. Just like in the river the length is a bigger advantage in reach once the line lands on the water than the extra distance you would get by casting. That extra foot and a half gives me an extra 3 feet of reach to lift my line over waves in the surf and over back eddies in the tidal rivers and estuaries to keep my fly in the water where I want it.