I can recall having been so intimidated by Superstar Saga's final boss that I turned around a trained the Brothers to level fiftysomething before attempting and acheiving a prompt victory. Now that Mario and Luigi are both at level 99 and posess stats well into the 400's, my fastest time to obliterate Bowletta stands somewhere slightly below two minutes.
Unnescessary boasting aside, my other levels are pretty similar to the above. Around 42 in Partners in Time, maybe 40 in Paper Mario:TTYD, and near the maximums of 27 and 30 in Paper Mario and Super Mario RPG, respectively.