I have a 9' 7wt and an 11' 7/8wt both work well on Erie tribs and Ontario tribs but the 11' is my first choice 99% of the time. I fish a couple VERY small Ontario tribs and the shorter rod is better suited for them. I would say that if you plan fishing mostly tribs like the Catt. then you won't be sorry going longer rather than shorter.
Hey... why not get both...You can never have too many fly rods.