Yes, I have tried the R19 S-- rake 8cm in under 15. Normally I would like this fin, but I've found this year now sailing a 12m Gaastra (versus 10.7m NP as biggest last season) I have too much power so I like to go smaller on the fin and use R13 70 when its under 15 knots.
You are right, a lot of people will find the R13 not enough power in the light wind however I am finding I do have enough power with the way I setup my gear (each to their own I guess).
The results on my R19 depended on which R19 I tried however; my own one (one of the earliest available, purchased during 2006 FW Worlds in Korea) I found had great height upwind but didn't have the speed I wanted. Down wind it was great. I tested another R19 of Hubert (POL-25, can't remember how to spell his last name!) which really had great speed upwind and the same height which was nice, but I couldn't get my R19 to perform the same as this. So I gave up to use my R19, however there's still many people using it successfully, I think you just have to setup your gear for this fin specifically.
Btw, Jesper Vesterstrom raced a couple of races at an event in Australia a few weeks back and used the standard Drake fin (R19 shape) and smoked us. So I think the R19 foil is good, it must just depend on the layup you have in your R19 as to its performance.
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