“Heroes of Might and Magic V: Tribes of the East”

Level 40? I haven't, but someone probably has. There isn't a specific topic where this is discussed because it's a rather useless endeavor. Sure, on certain maps, mapmakers create conditions for this, but it's only done for fun, to create an uber-hero. I doubt, however, that you can reach level 40 on standard maps, unless you specifically wait for neutral weeks and spend about 50 years of game time leveling up on them. However, it's quite common to fill all the skill slots for a hero: for example, in the fifth campaign of the original game, or in the Ser9K campaign "Dragon Wisdom".