Super Conductor Tyranno, one of the few monster with over 3000 Original ATK.
The "Rule of 3000 ATK and DEF" is a general rule that few monster cards have an original ATK or DEF of over 3000. Those that do typically have Special Conditions for being Summoned, to limit the cards. This rule is similar to the "Level 4 ATK and DEF Rules", however more flexible.
Over 3000 ATK
A very small number of monsters with over 3000 ATK can be Normal Summoned without special conditions, and with very few exceptions (such as "Super Conductor Tyranno"), they have negative side effects that can hamper their usefulness.
Neo Aqua Madoor is a 1 Tribute 3000 DEF Normal Monster.
Notably, all monsters with 3000 or higher ATK are usually the trump cards of their series: "Horus the Black Flame Dragon LV8" for the Horus LV monsters, "Volcanic Doomfire" for the Volcanics Series, "Ancient Gear Golem" for the Ancient Gears, "Judgment Dragon" for the Lightsworns, "Cloudian - Eye of the Typhoon" for the Cloudians and "Vampire Genesis" for the Zombies (just to name a few).
Monsters with 3000 ATK or more are usually used towards the end of a duel, as a last resort (such as "Gladiator Beast Heraklinos" in a Gladiator Beast Deck), although sometimes the deck's focus will be on summoning that card (commonly seen with "Valkyrion the Magna Warrior"). "Super Conductor Tyranno" is sometimes included in beatdown decks, as they have very few ways of stopping extremely high ATK monsters.
Over 3000 DEF
Monsters with 3000 DEF points are plenty, some with very low ATK and 1 Tribute (such as "Labyrinth Wall" and "Millennium Shield"). However, cards with over 3000 DEF points are rare and usually are good for both attacking and defending.