Who can beat Superboy Prime in a pyschical match up?

Only heralds or trans characters.

Who can beat him?

In trans or below? No one.

Already happened.

Just call the Teen Titans, lol. They'll assrape him good.

In a slugest and speed equalized? Potentially, other silver age kryptonians. Forum-Amazo. H/P Doomsday. Hulk can if given enough time