NSA slugs are a little harder lead alloy fwiw. My guns that have a tighter pellet choke didn't like them. Switching to a slug liner with less choke on my fx made it love them. Do you have .250 or .254?
Looking at the avenger specs its rated as a 45 fpe gun in 25. You're not too far off from 725 fps to get that 45 lb ft. Maybe lightly silicone lube a few slugs and shoot a group over the chrono and see if it helps or hurts accuracy or velocity? Maybe
If it's got a trajectory you can deal with, ive found I wasted my time and made guns less enjoyable chasing minimal velocity or energy gains if that makes you feel any better. I turned my slug shooter down 200 fps to avoid going transonic in certain weather. How far would you like to shoot?
When I had my impact turned up as far as I could for a similar weight slug, it wasn't fun anymore and not nearly as precise. My mrod is a similar story. Tight choke, similar speeds to you and not enough accuracy for me....also 25 cal but the slugs were 35 grains at the time. Heavy jsb pellets (i call them low bc slugs) were the remedy