What model of Daystate HP is it? Your effective range is going to depend on your ability to tune your rifle, and your ability to shoot it accurately. Also, on whether you are gonna be taking body or head shots. With rabbits I prefer head shots, because I don't wanna ruin any meat. I think you said it best, you have more testing to do. You need to find a pellet or slug that consistently drops within 0.5" at your given range. As long as you are not detuning below 20FPE, penetration shouldn't be too much of a concern. With my .25 I would feel comfortable shooting at to about 80yds without any issue, and 100yds on a good day taking head shots. As the previous comment stated though, a lot of time with rabbit you can stay inside 50yds, maybe 80 if they are exceptionally cautious. If 50yds, is all you feel comfortable with right now, there is nothing wrong with sticking to that until you feel comfortable with the tuning on longer shots.