Thanks for your suggestions!For the Shifter Kart I rarely drive "kart" tracks, which probably work better for single gear lower power (50cc?) karts, but instead drive tracks like Mills Short, Kicevo, Okayama Piper, Maze, etc. Usually club or drift tracks shorter than 4km. Check my resources and you'll see all the tracks for which I've made kart friendly AI lines.
Your 125 kart works fine with karting tracks. I tried castelletto, wuhan, brasilia (which are the best you can find imho) and the power is just right because there are long straights where you can unleash the power. I got the inspiration from pCars, which uses shifter karts for small karting tracks, which works to me.
There are other tracks that work for karting: VIR patriot, Knockhill, Modena are other examples. Thing is I wanted to keep the kart championship quite small in order not to bore the player. Secondly, i thought of a national karting trophy, so it would be odd to race around the world. I love your AI lines, though I wanted to keep the download size small and permanent; If the player goes to the same track next season with a "real" car, it would have to redownload the correct AI line and it's not really user friendly.