Back in the day I use to run my 11 naish nalu as a thruster ,large FCS alround ,never spun out and push the rear forward for more looseness .you have a lot of rail in the water so shouldn't need too big a fins ,I stood up the tail and flicked it around

I never liked the Quobbas either ,because I always am trying to slow my board down for moves ,tried them many time ,
I like AM1 shapers .with flex ,a lot nicer in choppy faces ,full carbon fins I find too stiff and harder to use ,I have a 6.5 rear Hop is you want to try it ,made for fin tracks ,