I have a 5'10" x 19 3/4" x 2 5/8" 1980 Retro Twin that MR shaped, and a 6'0" x 19 7/8" x 2 7/16" Super Twin that Rick Rock shaped. (I'm 6'1, 170 lbs.) The main difference is the Super Twin is a modern shortboard with concave, etc. and the Retro Twin is a retro model with wide point forward, deep vee, etc. The Super Twin I have was the latest computer file and has a flattish deck and the rails seem more high-volumed; I could have gone an 1/8" thinner no problem. But I really like the Super Twin, I instantly clicked with it, it's fast and turns freely and is user friendly. For me, there is a learning curve with the Retro Twin, and I haven't clicked with it yet. That's obviously my problem. It seems to need constant rail to rail movement to generate speed and I haven't been able to devote enough time to figure it out. Not sure if this helps or not; either way you go and whether MR or RR shapes it, ...lost San Clemente does nice work with these boards.