Gotta go fast!
If you like Isekai Speedrun, you might also like these Japanese webnovels or light novels with similar elements in setting, characters, or general atmosphere:
1) Isekai Canceller
2) Kono Sekai ga Game da to
3) My Death Flags Show No Sign of Ending
4) The Latest Game Is Too Amazing
5) Tsuyokute New Saga
Or if you don't like Isekai Speedrun, maybe these stories are closer to what you're looking for.
Two Finnish speedrunners that were early inspirations for the Isekai Speedrun webnovel: check out TheKotti for his Arabian Nights and Hitman runs, and GarishGoblin for his Halo runs.