Not Kevin, but here is a little about the techtonics fin that I have. I have an 2008 iS 111, but only wanted to invest in one fin, so I bought a Tomcat 42. I probably would have gone for the Goldwing, but it only comes in sizes 26-38 cm. I weigh 79kg
However, I really like the Tomcat. Seems fast and never spins out. If pushed out, it comes right back without pulling it in. The 42 is a little small for my Maui Sails 8.4 TR3. Perfect for my 7.6 TR4 and a little big for my 6.6 TR4. I don't slalom race much, mostly freeriding so I like a larger fin to help with the upwind work. I have been over 30 knots (GPS) with my 6.6 in choppy water with good control with the 42cm fin.
I hope this helps a little. I don't think Kevin uses Techtonics so he may not respond, but if you post on the Free Forum, you may get more responses.
My Tomcat 42 is significantly better than the Drakes that came with my board (38 & 44). However, I have seen some recent reports that the new Drakes may be better than the 2008 models. I don't know if they changed the design for '09 or not, but the '08 fins have BIG spin out problems.