I used the x-twins 16.5cm on my JP 83lt twin for two seasons and love them
in all conditions 3.9/5.3
well recomend them
never had any spin, slide or bounce on bottom turns but mabe a bit to loose on top turns
i'm now looking for right set up for my thruster
would sugest sending Olaf at MUF a email and ask him about the right size for you and your conditions
pretty sure Koster uses 16.5cm but ask Olaf he will tell you what he uses and for what conditios