My first time through, I won around L50. However, I have done one of those 1/5/17 things on my cart. It's a good challenge. The Nizbels are hell, and Lavos Form Two is nigh impossible.
And that's not the record. There have been reports of people winning at the mathematical minimum - Crono L1, Marle L4, Robo L16. However, all such games were done on an emulator, which IMO kills the whole point of the challenge, with the rampant savestate abuse and all.