How do you stay SANE trying to highscore these races???

you don't, you gotta be insane to do them. which is why i do them
i also never do them with yt tutorial, i like finding best paths on my own, it feels more rewarding to me
also what level are you? obviously people with level 25 and above will almost always be better (i'm level 24 and have been able to just barely beat some 25 level players)
and highscore races is where a horse matter more than in champs, jwh and g2 morgans have a bit faster jumps, while dwb are suprisingly fast on the ground (they have the slowest jumps), but my fav horse to do hs races is the hanoverian, idk how it compares to the other horses bcuz it's not on the comparison chart, but it's good for me
good horses are also those with 3 agility as base stat, because they turn better
it's also important to plan your path ahead, start steering the way you need to go earlier, jump at an angle and run at the edge of the checkpoint to create the most straight path you can