I’ve run both the Tillet T11t and the standard OTK seat in my Racer 401. Those seats are identical, so I ended up going with the standard OTK seat since its cheaper. As far as seat position goes, I’ve tried the factory recommended seat positions for my height as well as a couple seat positions recommended by 2Wild Karting. Since my height is exactly 170cm, I tried both the 160-170 and the 170-180 seat positions, finding better performance with the 160-170 seat position since I mostly race KPV’s. The 2Wild seat positions were very close to the factory recommended positions, the main difference being the ease of installing the seat when using the 2Wild positions, and performance being nearly identical to the factory positions. If I was racing an X30 I think the 170-180 seat position would work better. Kartingmagazine.com had a good read about a test they ran comparing the 3 seat stiffness of the Tillet T11 on a Tonykart Racer. I believe they found the stiffer the seat, the looser the kart ran in the rear. I’m sure this is not true for other karts though.