Supes stomps, he takes on much more powerful villains than Nimrod, such as Amazo and Doomsday etc.... Nimrod is an X-Men villain, totally different leagues.
Superman probably wins if he decides to end it as fast as possible. Otherwise Nimrod analyzes his weaknesses and takes him down by replicating red sun emission spectrum.
Superman 7/10.
(Note: kryptonite radiation might take some time for Nimrod to synthesize but the spectrum of a red sun is well-known and easy to reproduce for someone like Nimrod.)
This is basically a fight against the clock for Supes. Nimrod is a weakness-exploiter and Superman has some of the most notorious weaknesses of all herald+ level characters.
And it is not easy to put Nimrod down, either. Rogue once absorbed the powers of the X-men; teleported Nimrod's arm off and then smashed him to bits with the combined powers of Colossus and Ms. Marvel.. and Nimrod immediately repaired himself the next panel.