I had C-drives in my 8'10 and 9'1 Acid. I liked them in some conditions, but it seemed to me that at high speed on the bigger waves (>24 kph by my rip curl watch) they made it harder to turn. I have tried quobba but not enough to comment. I am using Shapers AM2 now and I like them - they feel loose to me - a bit of sideways motion that I like.
I need to put the quobbas on my 9'1. I am 98 kg so I have been mostly riding my 9'1.
But I should have started this by saying that I know zero about fins.