Josh, it would be helpful to know your weight to recommend fins, however, in general, when looking at FCS-style fins you need to be looking at the #3s (i.e. PG3, UL3, PC3) for behind the boat; Other than that I would suggest some getting some nubsters for the rear. Actually, if you PM me, I will cut you a deal on some PC3 and nubsters. I have a box of them sitting here. I don't sell that many FCS fins anymore, mostly Futures and other specialty brands. Wakeboard companies are really on the people using FCS style boxes in wakesurfers.
Yes, premium fins do make a difference, they tend to be lighter, and have a more responsive flex. Without going into a lot of physics, your fins are 'loaded' (with energy) when riding. The loading and releasing is what makes are fins, albeit only one aspect of how they work, is important.