I would drop to 75 gr and try 3 shots, then 80 gr and try 3 shots, then 85 and try 3 shots:

clean between each shot!!!

that is how I experiment with each new gun, bullet, and powder I try. Maybe you can get even better groups with 75,80, or 85 and use less powder (less expensive!)

it is not unusual for the group to move significantly with each change. That explains why the group moved to the left when you went from 70 to 90 gr. Don’t worry about moving your sights until you decide for sure on how much powder you will use to hunt with. Then move your sights.