The Starboard fins are designed by the best of the best and in that sense fully competitive. A lot of work has been put into the manufacturing too. But in the end, when it comes to small margins and extreme fine tuning, I think most serious racers will say a hand made top of the line product like Deboichet give a certain edge.
Personally I only sail slalom recreationally and for me the original fins works very well. I would probably be able to feel a slight difference in some situations with a genuine Deb fin, but prefer to spend time working on my technique and trim than to worry about it. As always, there is lots of psychology in this. If you beleive there is "something wrong" with your fin, it wil no doubt have an effect on your sailing. I did choose to get some more sizes of the Drake fins instead and I think this will help me delevelop my understanding of my own sailing and about board/sail trim better than to shell out for one single top of the line fin.
I think Ian can say more on this. He's both a better slalom sailor and involved in fin testing and design.