Turbo fins
 

I can tell turbo fins make a big difference,are there different sizes?
I was told by a BWEr to get the ST fins.

There are stock fins, ST fins and Turbo Fins, the ST fins use the same mast as the stock fins but look like a slightly shorter Turbo fin.

http://www.kayaksandpaddles.co.uk/ca...aks-fins-2.jpg

What's the difference performance wise?

Bigger is better...get turbo...

I bought my Outback from OEX with the turbo fins already installed so I can't speak from experience but in speaking with others those that purchased Hobie's with stock fins and upgraded state that they did notice a difference in performance. The same can be said of the stock and sailing rudder
stock: turns on a dollar
sailing rudder: turns on a dime.

I have an outfitter with two drives. I stripped off a few gears on my turbo and had to wait for a new set to switch out. It had been a while since I used the stock fins so I just grabbed the other drive and went out. It felt like I didn't have fins moving at all. BIG difference between stock and turbo fins. Turbo fins take more power to push but the torque trade off is worth it.