8" is way to short for that board. You may lose control when you don't want to. Increasing the length will give you more forward drive (Needed on our type waves) but will make it a bit harder for you to turn. That's where you can go with with a more flexible fin. You can also move the fin towards the front to loosen her up, go to far and there goes your drive. - Forward loose, rearward drive. Bring a screwdriver to the beach with you and just try it out.
Stiffer fins are faster but it is harder for you to turn. Flexible fins are more maneuverable but it sacrifices speed if it increases in flexibility along with nose riding ability.
Thanks Hyatt. I guess I was just seeing if I could get by with what I have. Just got the 10 footer and the fin it came with (not the 8") is really heavy and super stiff. I feel like it really strips all of the livelyness out of the board. Looks like I'll be needing to spend a little more $. Thanks for the link too.
I would actually recommend the FCS Fatboy. I have a really big 9'5" SOD custom. When I first got it I had a 10" rainbow fin and couldn't get it to turn to save my life. I tried a friends 9" Fatboy and loved it. Thats what I've had in it for the past year and don't plan on changing. I can turn the board, but it still holds my weight (230lbs) on the nose. Some of that is the board, but the fin helps a lot.
Some shops do free FCS trials, so see if you could give one a try before you pay for it.