With Queen's bounty being so high (and his portrayal being similar to King) i guess the difference between them isn't that much, but King and Queen are special, they are not just Kaido's most loyal Commanders for decades but they have acknowledgment of important events for the OP world, even having major participation of these events, thats Queen.
King, according to Big Mom, is the last living from an extinct race long ago, both King and Queen also have unique Devil Fruits and powers, Queen is probably the strongest Cyborg out there with a rare and strong Brachio DF, King has 2 giant black wings, potentially a competent swordsman and also a user of a rare Pteranodon DF, with the epithet of "Wildfire". They are mysterious, Marco isn't
King's bounty could be 1.4Bi or a little bit higher (like 1.43Bi), otherwise i think it will be something between 1.36~1.33Bi, lower than Marco's