First I would have said try to edit slowly the one world races with a maximum player number per world (as it's possible in /buildmode, it might be edit'able, right?) but yeah I guess less slots is the best idea, since with more players pings start to be annoying... Although don't you think about 48 is better? With 48 players, there's always a few who aren't in /race anyway, pings are still correct usually, and that may not even need a 2nd server.
Oh and I also thought about sth that might be a bad idea... maybe make a lobby when we join, that give us the choice to go /race, /stunt, /tv, /dm etc, instead of directly in /race so a bit less players will be directly messing up in /race. But it might be a bad idea since the main purpose of the server is racing.