since you'll be using it for local lakes I would suggest going for the 9'
For the most part you would select a shorter rod if you needed to cast in tight situations (i.e. trees, canyon walls, overhanging trees, anything that will limit a back cast really)
if you're fishing a lake from a boat or dock then you don't have to worry about the length of your rod. and you may want the extra length for making those longer casts
which would be harder with a shorter rod. If you plan on fishing smaller streams making short delicate casts then you may want to look into the shorter rods in my opinion
My uncle picked up that rod a while ago in the 9' 5wt. Seems to be a good rod and at a good price, although he pulled it out of the case the other day and the tip section was broken somehow... but st.croix's warranty will take care of that. Was an odd thing as he didnt noticed it was broken until he pulled it out of the case at the river and it was missing? not sure how that happened..