Rabbit Hunting distances - predictable shots

My opinion-It depends on what kind of consistent accuracy you personally can achieve at a given distance in real world conditions (shooting offhand or off sticks) rather than power. In my experience I rarely need to to take a longer shot than 45 yards on even wary rabbits. I usually fill my bag with shots anywhere from 10-15 yards to 30-35 or so.
 
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.
 
Pellets can lose stability as they travel downrange. One gun I have will shoot one design of pellets very well 45 yards (sub 3/4 inch) but at 55 yards, those pellets will not stay on a 6 inch target. You can see in the scope when they spin out of controlled flight. It takes time, lots of ammo and air to feel out the best effective range for your gun and your tune.
 
Pellets can lose stability as they travel downrange. One gun I have will shoot one design of pellets very well 45 yards (sub 3/4 inch) but at 55 yards, those pellets will not stay on a 6 inch target. You can see in the scope when they spin out of controlled flight. It takes time, lots of ammo and air to feel out the best effective range for your gun and your tune.

Twist rate might be too high, spinning the pellet too fast. Have you tried slugs in that gun?
 
Yes, and I was not impressed. The mk ii pellets shoot better than the mk I, but not as well as the Seneca domes. Those seneca have shot as well as 5/8 inch at 100 yard. Yes, a unicorn 5 shot group but still head and shoulder better than the JSB. Every gun can prefer different pellets, and some pellets only shoot well in a narrow range of velocity. It takes time, air and ammo to find what is best for your gun. 
 
Bullet trajectory really comes into play beyond 75 yards. That would be my limit especially if there is ANY wind. I consider myself to be an average shot. If you become an expert with your rifle you could easily stretch it out but how many opportunities will you get beyond 75 yards as it is.
I think you need to determine what you personally can do and I’d suggest not paying much attention to what you read on the forum. We have some people posting who are clearly well above average . It takes time and experience. A year ago 50 yards was a long shot for me. In a year I’ve invested considerable time effort and money and I’m now shooting mostly at 100 yards. BUT I’m not able to consistently measure or gauge the wind so at this time I would not take shots at game animals beyond 50 or 75 max.