NG+1 is a 2 or 3, if regular NG is a 5. I'm only up to and including Genichiro in NG+2 so far, but currently it's feeling like a strong 2. Partially because I've gotten more practice, and partially because I did Purification on NG+1, and the extra damage is melting all my enemies like butter. Depending on how hard you find it, you might want to kill as many bosses as you can every NG+ to make later runs easier. The extra purification boss can be fought regardless of which ending you're actually getting, I'm pretty certain, and Demon of Hatred can get pretty easy once you learn how you have to fight him. Same goes for Headless Ape. You could skip that one, but it's often pretty easy, and the extra damage can be huge.