the other general rule of thumb is that a oar should be around 2/3 the length of your raft...
so a 9ft mini-me=
9 X .66 = 6ft (don't think carlisle makes them that short for the heavy duty ones and 8' sounds kinda huge to me for such a dinghy.
16 x .66= 10.5
and as mania say allot of this depends on width of your frame and boat. it's just an indicator. personal preference needs to be factored too. taller people like me tend to like longer oars vs. shorter folk liking shorter oars.
I run 11ft ers on my 16fter but I like long oars. For a big water run like the GC you may like them for their power and ability to give you a strong brace. Downside for some is they are heavy if you are a sally.
Also, the carlisle breakdown oars work fine. Are they great feeling oars? No but they get the job done. I use them cuz I do a fly out type trip at least once a year and they are perfect for that stuff where they need to fit in small planes,ect