Be warned, this question contains serious end game spoilers. Don't read it unless you finished the game.
I just finished the second epilogue chapter, and I'm wondering now if I should finish the remaining open world stuff in the epilogue with John instead of Arthur, with an earlier save or a new game. So I'm mostly wondering if there are side missions that are not available after the epilogue, or any other differences compared to the early game. Is there any content that is exclusively available before or after the epilogue?