I haked down a set of bent 10 foot carlise oars to 7' 9" or something close to that for my sabertooth. When you get in a small boat the rule of thirds does not apply. The boat is so light that the oars do not take the levereage away from you like on a big boat. I could go all the way down to 7 or back up to 9 foot and anywhere in between. It is a lot like Dutchman and K2 said it really depends on how skinny the water is.
On a side note, once I cut down those aluminum oars I cut both end of and got to where they are double walled and now they are next to industructible
I am an American Whitewater member. One of 6300. There are an estimated 100000 paddlers in the U S. If you are not a member you should join. AW is fighting for our rivers everyday and could use some help.