Comparing the official 3.0 and 3.5 versions of the higher base modrons, the latter have one more Hit Dice and significantly better AC and ability scores.
Quadrone:
3.0 D&D
Medium-Size Outsider
Hit Dice: 4d8+4 (22 hp)
Armor Class: 16 (+2 Dex, +4 natural)
Abilities: Str 16, Dex 15, Con 13, Int...