Untill a couple of months ago, I had a Sonic 100 for a couple of years. It was a brilliant board (S100/7.6m/Evo 35cm is my all time favourit comb, 15 to 30 knots mile eater in any sea state). I'v just got rid of a load of sonics (125/100/90) & F159 for three new 08 iS's (76/111/144) to keep things simple. The Drake 34cm supplied with the S100 was not to good for me so I got an 05 Select Evo 35cm (for 7.6m Warp) and a 31cm Evo (for 6.8m Warp). Both these fins improved upwind loads. Also improved the ride through heavy chop. Maybe a fin change will help you out.