I have spent a lot of time on mid-length single-fin performance boards and have worked on several fin designs to optimize how they work. In the end, I refined the sizes down to just two: 7.25 and 8.0. For 66 – 76 with pulled-in tails, go with the 7.25 fin. For larger, wider boards in the 68 8.0 range, then go with the 8.0 fin. They are upright with a lot of base and lend themselves to no-frills power surfing.