"We 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 6’6” -  7’6” with pulled-in tails, go with the 7.25” fin.  For larger, wider boards in the 6’8” – 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."