MegaMan is 1 Megabit in size, MegaMan 2 is 2 Megabits, MegaMan 3 is 3 Megabits and Megaman 4 is 4 Megabits !! However, this doesn't continue any longer because MegaMan 5 and MegaMan 6 are also both 4 Megabits.
In Japan, a doujinshi manga (fan-created manga) of Rockman 4 is available. It follows the game's plot more or less straight through, but it's missing two boss encounters from the game: one from Cossack's citadel (the Wall Walkers), and one from Wily's castle (I forgot which). The manga was published by the manga label BomBom, and it's a rather rare find.
The "antagonist" of Rockman 4, Dr. Cossack, makes a guest appearance in Rockman 8! But wait! Before you go screaming about "I already beat that game! Where is he!?", he doesn't appear in the game, but in a manga series BASED on Rockman 8 that was released in Japan! Cossack's daughter, Kallinka, also makes a quick appearance in the manga.