Just recently obtained 2 fins which are impressing me no end.
They are fast, allow me to go up-wind and generally don't let go. (C3 Venom and Techtonic Goldwing).
However, as soon as the board hits a bit larger chop they lose traction.
I had a similar experience with a less performance oriented JP Weed.
I was hoping the more experienced guys could help me with an advice:
Would a FSW weed fin behave better in the chop?
What's the advantage of the wave/FSW curved fin shape?
Looking forward to some education.
The racked back fins are better for control & jibing the more upright fins are generally for speed! Talk to someone who knows there fins? 
I'm no expert on fin theory but the Goldwing and C3 venom are good fins.
The FSW and wave fins are curved to help turning.
Upright fins give more lift and help you point higher, and raked fins give more control and ease of gybing. Extra rake helps to shed weed and reduces lift. Sometimes using a weedy in chop gives extra control because it helps keep the board on the water - less lift. Moving your mast foot forward can help keep the board down too.
Are you too heavy on your back foot? This will cause you to spin out, especially over chop. You want to have the fin loaded up but not too much. Try to have your weight balanced between both feet when you are sailing square. This requires adjusting boom height, and mast track position. When you get it right, everything works so much better!
Also try to find a line between the chop that will keep your fin in the water.
Have a look at this thread.
www.seabreeze.com.au/forums/Windsurfing/Review/C3-fins-Venom-v-Sting/
The Goldwing is a fairly fine foil and needs to be well powered for best performance. I use a small one for downwind speed runs.
The venom has a softer tip and a bit more rake, so with those it's best to use a size about 2cm bigger than norm.
You may want to look at your technique as well, when you land a hop chop point the board down wind a little and not too heavy on the back foot.
Both these fins are slalom / speed oriented so like being powered. A freeride or FSW fin will be more forgiving.
