I have an 8'6"

ball by McT which is a shrunk down (like me) Fireball..
It goes really well with the std McT fins it came with but I'm trying a different setup which is a 6" centre fin with FCS H2 mediums as the side fins..Works really good..loose but comfortable

In essence though just get some fins from mates and play around and find which way you prefer

Std fin set for reference below..